One of the most personal decisions in mattress shopping is choosing the right firmness level. What feels perfectly comfortable to one person can feel like sleeping on a rock — or a cloud — to another. Firmness is highly subjective, and getting it wrong is one of the most common reasons people end up with a mattress they don't love.
This guide breaks down the firm vs soft mattress debate for Australian sleepers, covering how firmness affects sleep quality, spinal alignment, and comfort based on your body weight, sleeping position, and personal preferences.
What Do We Mean By Firmness?
Firmness refers to how much resistance a mattress provides when you lie on it. A soft mattress allows the body to sink in more, providing a cradling, enveloping sensation. A firm mattress pushes back against the body, keeping the sleeper closer to the surface. Most mattresses are described on a scale from 1 (softest) to 10 (firmest), with medium (around 5–6) being the most popular selling range.
Important note: firmness is not the same as support. A mattress can be soft on the surface but still have excellent internal support structures. Conversely, a very firm mattress might not actually provide good spinal alignment if its support layers are poorly designed.
Firm Mattresses: Who Are They For?
Stomach Sleepers
Stomach sleepers are the group most often recommended a firm mattress. When lying face down, a soft mattress allows the hips to sink lower than the chest and shoulders, creating a U-shaped curve in the spine. Over time, this can cause serious lower back pain and discomfort. A firmer mattress keeps the body in a flatter, more neutral position.
Heavier Sleepers
People over 100kg often find that a mattress rated as 'medium' by a manufacturer actually feels quite soft under their body weight. A firmer mattress provides better resistance and is less likely to develop body impressions prematurely. If you're a heavier sleeper who prefers a softer feel, look for mattresses specifically rated for higher weight categories.
Back Sleepers Who Prefer a Flat Feel
Some back sleepers prefer the feeling of sleeping on a stable, flat surface rather than contouring foam. Firmer mattresses suit this preference and can provide excellent lumbar support if the firmness is appropriate.
Soft Mattresses: Who Are They For?
Side Sleepers
Side sleepers put significant pressure on their hips and shoulders — the widest parts of the body. A soft or medium-soft mattress allows these pressure points to sink in slightly, relieving the pressure and keeping the spine in a neutral alignment. Sleeping on a mattress that's too firm as a side sleeper often leads to shoulder pain, hip discomfort, and disrupted sleep.
Lighter Sleepers
People under 65kg don't exert enough downward force to compress a medium or firm mattress to the same depth that a heavier person would. A mattress that feels medium to most people might feel quite firm to a lighter individual. Softer options provide appropriate contouring for lighter body weights.
Those with Pressure Point Sensitivity
If you have conditions like fibromyalgia, arthritis, or bursitis, a softer mattress surface can significantly reduce pain by distributing pressure more evenly across the body. This is one area where memory foam mattresses — which tend toward a softer feel — have a particular advantage.
What About Medium Firmness?
Medium mattresses (roughly 5–6 on a firmness scale) are the best-selling category for a reason — they suit the widest range of sleepers. Most back sleepers, many side sleepers, and combination sleepers tend to do well on a medium mattress. If you're unsure what firmness to choose, medium is a safe starting point, especially if you can take advantage of a free trial period.
Many Australian mattress brands now offer adjustable firmness. Ecosa lets you rearrange internal foam layers to change the firmness. Sleeping Duck Mach II lets each side of the mattress be configured independently — ideal for couples with different preferences.
Firmness by Sleeping Position: Quick Reference
- Side sleeper: soft to medium (4–6)
- Back sleeper: medium to firm (5–7)
- Stomach sleeper: medium-firm to firm (6–8)
- Combination sleeper: medium (5–6)
Does Body Weight Affect Firmness?
Yes, significantly. The industry commonly uses three weight brackets as a rough guide:
- Under 65kg: sleep lighter on the mattress surface, often need a softer firmness than the stated rating suggests
- 65–100kg: the average weight range that most firmness ratings are designed around
- Over 100kg: sink further into the mattress, often need a firmer rating to get the same feel and support as lighter sleepers
Firmness and Back Pain
This is a nuanced area. For decades, conventional wisdom said that a firm mattress was best for back pain. Research has since shown this isn't always the case. A study published in the Lancet found that medium-firm mattresses were more effective at reducing chronic lower back pain than firm mattresses. The key is spinal alignment — whether soft, medium, or firm, the right mattress for back pain is one that keeps your spine in a neutral position throughout the night.
Trial Periods and Firmness
Because firmness is so personal, one of the most useful things you can do is buy from a brand that offers a proper trial period. Most reputable Australian mattress brands offer 100–120 nights, which gives your body time to adjust and gives you enough time to genuinely evaluate whether the firmness works for you. Don't judge a mattress in the first two weeks — it can take time to adapt, especially if your old mattress had a very different feel.
Our Verdict
There's no objectively superior firmness level — it entirely depends on how you sleep, your body weight, and your personal preferences. Side sleepers and lighter people generally do better on softer or medium mattresses. Stomach sleepers and heavier people generally need more firmness. Back sleepers and couples often land on medium as a good all-rounder.
If you're unsure, choose a medium mattress from a brand with a long free trial period, and give it at least 30 nights before forming a firm opinion.
Firm vs Soft Mattress: Head-to-Head Comparison Table
| Feature | Firm Mattress | Soft Mattress |
|---|---|---|
| Surface Feel | Minimal sinking, flat, supportive | Cradling, enveloping, pressure-relieving |
| Best For | Stomach sleepers, heavier individuals, back pain relief | Side sleepers, lighter individuals, pressure sensitivity |
| Spinal Alignment | Keeps spine neutral when matched to body weight | Allows natural curvature at hips and shoulders |
| Durability | Often resists body impressions longer | May develop body shapes sooner with heavy use |
| Motion Transfer | Generally isolates movement well | May transfer movement more readily |
| Temperature Regulation | Typically cooler, less heat retention | Can sleep warmer depending on materials |
| Price Range (AUD) | $600–$2,500 depending on brand | $600–$2,500 depending on brand |
Performance Comparison: Key Areas
Comfort and Pressure Relief
Soft mattresses excel at pressure point relief, making them superior for side sleepers and those with joint sensitivity. Firm mattresses provide stability and a flat, responsive feel that many stomach sleepers and heavier individuals prefer. Neither is universally "more comfortable" — it depends entirely on your body and sleeping position.
Motion Isolation
Firm mattresses generally isolate motion better because they have less sinking, so movement from a partner is less transmitted across the surface. Soft, foam-based mattresses also isolate well due to their material properties, though some edge movement may be more noticeable.
Temperature Regulation
Firmness alone doesn't determine heat retention — materials do. However, softer mattresses (often memory foam) tend to sleep warmer. Firm latex or pocket-spring options typically run cooler, which matters if you're a hot sleeper in Australian summers.
Edge Support and Durability
Firmer mattresses with robust edge support resist sagging better over time. Softer mattresses may develop body impressions sooner, particularly near the edge, though quality construction minimises this issue.
Final Verdict by Sleeper Type
- Couples with different preferences: Choose medium firmness or adjustable options like Sleeping Duck Mach II
- Side sleepers: Soft to medium (4–6) — prioritise pressure relief
- Hot sleepers: Firm latex or spring options; avoid memory foam if heat sensitivity is an issue
- Budget buyers: Medium firmness offers the broadest appeal and best value across Australian brands
Our Recommendation
Start with medium firmness unless you have a clear reason not to — stomach sleeping, significant weight, or diagnosed side-sleeping pressure issues. Use your brand's trial period to confirm. If needed, adjust: Ecosa and Sleeping Duck offer this flexibility, making them excellent choices for uncertain buyers.