⚡ Quick Firmness Finder
Side sleeper: Medium to medium-soft
Back sleeper: Medium to medium-firm
Stomach sleeper: Medium-firm to firm
Combination sleeper: Medium
Adjust one level softer if under 65kg; one level firmer if over 95kg.
Why Getting Firmness Right Matters
Firmness affects two things that directly impact sleep quality: pressure relief and spinal alignment. Too firm and the mattress pushes back against your hips and shoulders, creating pressure-point pain. Too soft and your spine sags into the mattress, loading the lumbar vertebrae and causing the morning back stiffness that millions of Australians mistake for "just how they are."
The right firmness keeps your spine in a neutral position — not arched, not flat — while allowing bony protrusions (hips, shoulders) enough give to sit comfortably against the surface. What "right" means differs by sleep position and body weight.
Firmness by Sleep Position
Side Sleepers — Medium to Medium-Soft
Side sleeping puts concentrated weight on the hip and shoulder. These need to sink into the mattress surface while the spine stays neutral. Medium to medium-soft is the standard recommendation — enough give for pressure relief, enough resistance underneath to prevent full spine collapse.
The warning signs you've chosen the wrong firmness as a side sleeper: waking with hip pain or a numb shoulder (too firm), or waking with lower back pain and a visible sag under your waist (too soft).
Back Sleepers — Medium to Medium-Firm
Back sleeping distributes weight more evenly than side sleeping. The priority shifts from pressure relief to lumbar support — the mattress needs to fill the natural inward curve of the lower back without letting the hips sink below the chest level. Medium to medium-firm achieves this. A very soft mattress will let the hips drop too far; a very firm mattress will leave the lumbar gap unsupported.
Stomach Sleepers — Medium-Firm to Firm
Stomach sleeping is the hardest position on the spine because the hips — the heaviest part of the torso — push down furthest. On a soft surface, the hip drops significantly below the chest, creating lumbar hyperextension that causes lower back pain. A firm surface keeps everything level. This is the one sleep position where "firmer is better" genuinely applies.
Combination Sleepers — Medium
If you regularly sleep in multiple positions throughout the night, medium is the pragmatic middle ground that doesn't fail dramatically in any position. The Koala Original and Emma Original are both designed specifically for this common Australian sleep pattern.
How Body Weight Changes the Recommendation
Firmness labels are relative to an average body weight (approximately 70–80kg). The same mattress feels noticeably different at different weights — a "medium" at 75kg feels medium-firm at 55kg and medium-soft at 100kg.
| Body Weight | Side Sleeper | Back Sleeper | Stomach Sleeper |
|---|---|---|---|
| Under 60kg | Soft to medium-soft | Medium-soft to medium | Medium to medium-firm |
| 60–90kg (average) | Medium to medium-soft | Medium to medium-firm | Medium-firm to firm |
| 90–120kg | Medium to medium-firm | Medium-firm | Firm |
| 120kg+ | Medium-firm | Firm | Firm (specialist mattress recommended) |
How Australian Brands Compare on Firmness
There's no standardised firmness scale in Australia — each brand defines its own. Based on consistent customer feedback across Australian reviews, here's how the major brands compare:
- Koala Original — Genuine medium. The most consistently described as "true medium" by Australian reviewers across weight ranges.
- Emma Original — Slightly softer than Koala. Australian reviewers often describe it as medium to medium-soft in practice.
- Ecosa — Adjustable across three configurations, ranging from approximately soft to medium-firm.
- Sleeping Duck Mach II — Adjustable per side from soft to firm. The firmest setting is the firmest option available in the Australian in-a-box market.
- Ergoflex 5G — Medium-firm. Described consistently as firmer than Koala and Emma, appropriate for back sleepers and lighter stomach sleepers.
What to Do When Couples Need Different Firmness
The honest answer is: the Sleeping Duck Mach II is the only Australian mattress with genuine per-side firmness adjustment. One side can be set soft for the side-sleeping partner; the other firm for the stomach-sleeping partner. This isn't a minor feature — for couples with genuinely different needs, it's the only solution that doesn't require one partner to compromise their sleep quality.
If the Sleeping Duck's price is a stretch, both partners choosing the same medium mattress (Koala or Emma) and supplementing with a mattress topper on the softer-preference side is a lower-cost workaround.