Firmness is the thing people agonize over the most and get wrong the most often. Here’s why: most people think firmness is about comfort preference — “I like a soft bed” or “I need something firm.” It’s actually about sleep position. Your body doesn’t care what you like. It cares whether your spine stays straight.
The Five-Second Test
Lie on your side on your current mattress. Have someone look at your spine from behind. If it curves like a banana (hips sinking, shoulders high), your mattress is too soft. If your waist gapes open (hips pushed up), it’s too firm. Straight line from neck to tailbone? You’re good.
Do this test before you read another word about firmness scales. What you actually need might be different from what you think you prefer.
Firmness by Sleep Position
| Your Position | Best Firmness | Because |
|---|---|---|
| :– | :–: | :– |
| Side sleeper | Medium (5-6/10) | Shoulders and hips need to sink 3-5 cm |
| Back sleeper | Medium-Firm (6-7/10) | Lumbar curve needs active support |
| Stomach sleeper | Firm (7-8/10) | Too soft = lower back hyperextends |
| Combination (all three) | Medium (5-6/10) | Compromise toward side-sleeping needs |
Side note on body weight: If you’re over 90 kg, go one step firmer than the chart suggests. You’ll compress the mattress more than average, so “medium” to you is “soft” in practice. If you’re under 55 kg, go one step softer — you won’t compress enough to get the intended support.
The Firmness Scale People Actually Use
Forget the 1-10 numbers. Here’s what matters:
Too soft = You feel like you’re sleeping in a hammock. Getting out requires a core workout. Lower back aches by morning.
Medium = You feel cradled but not swallowed. Shoulders and hips dip slightly. Easy to roll over.
Medium-firm = You feel supported with a thin layer of give. Minimal sink. This is where most back-pain research points.
Too firm = You feel like you’re on a carpeted floor. Shoulders and hips press painfully. Numbness at pressure points.
The Goldilocks zone for most people is 5-7 out of 10. But your sleep position picks the number, not your preference.
How Moona Models Map to Firmness
| Firmness | Moona Models | Best For |
|---|---|---|
| :– | :– | :– |
| Medium (5-6) | Bloom MB001, MB002 / Lullaby ML001 | Side sleepers, lighter body types |
| Medium (5.5-6.5) | AeroSeries MAS001, MAS002 / ChillTek MC001 / Serenity MS001 | Combination sleepers, couples |
| Medium-Firm (6-7) | OrthoSync MOS001, MOS002 / Eclipse ME001 / Serenity MS002 | Back sleepers, back pain |
| Medium-Firm to Firm (7-8) | Plush Harmony MPH001, MPH002, MPH003 | Stomach sleepers, heavier body types |
If you have no idea where to start: pick Medium-Firm. Two-thirds of people end up there. And you can always add a topper for more softness — you can’t firm up a mattress that’s already too soft.
Couples With Different Preferences
This is the most common dilemma and the answer is simpler than people make it: go with the firmer option and add a split topper on the softer side. Two single-size toppers side by side give each person their own firmness without buying two mattresses.
If the gap is extreme — one wants soft, one wants firm — a hybrid mattress with a thick comfort layer is the best compromise. The springs provide the support the firm-sleeper needs. The foam provides the sink the soft-sleeper wants.
Stop overthinking the number. Do the side-lying spine test tonight. That’ll tell you more than any firmness guide ever will.
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