Choosing the right mattress firmness is one of the most important decisions you'll make when shopping for a new bed. Get it wrong, and you could spend years dealing with poor sleep quality, morning aches, and chronic discomfort. Get it right, and you'll wake up refreshed and pain-free every day. The challenge is that firmness is highly personal—what feels perfect for one person might be completely wrong for another.
In this comprehensive guide, we'll explain exactly how to determine your ideal firmness level based on your body type, sleeping position, and personal preferences. By the end, you'll have the knowledge to confidently choose a mattress that provides the perfect balance of comfort and support for your unique needs.
Understanding the Firmness Scale
Mattress firmness is typically measured on a scale of 1 to 10, where 1 is extremely soft (like sleeping on a cloud) and 10 is extremely firm (like sleeping on a floor). Most commercially available mattresses fall between 4 and 8 on this scale, as the extremes rarely suit the average sleeper.
Here's a breakdown of the general firmness categories:
- Soft (3-4): Deep contouring, significant sinkage, ideal for side sleepers under 60kg
- Medium-Soft (5): Good pressure relief with moderate support, suits lighter sleepers
- Medium (6): The most popular choice, balances comfort and support for most people
- Medium-Firm (7): Solid support with less sinkage, preferred by back sleepers
- Firm (8+): Minimal sinkage, strong support, best for heavier individuals and stomach sleepers
Firmness perception is subjective. A mattress that feels medium to a 90kg person might feel quite firm to someone weighing 55kg. Always consider your body weight when interpreting firmness ratings.
How Body Weight Affects Firmness Choice
Your body weight significantly influences how a mattress feels and performs. Heavier individuals compress foam layers more deeply, making mattresses feel softer than their rating suggests. Conversely, lighter sleepers may not compress foam enough to experience proper contouring on firmer mattresses.
Lightweight Sleepers (Under 60kg)
If you weigh under 60kg, you'll generally need a softer mattress than average recommendations suggest. Lightweight sleepers don't exert enough pressure to fully engage firmer support layers, which can result in an uncomfortable, "sleeping on top" feeling. A mattress rated 4-6 on the firmness scale typically works best, allowing proper contouring around shoulders and hips without feeling too resistant.
Average Weight Sleepers (60-100kg)
Sleepers in this weight range have the most options available. Standard firmness recommendations apply, meaning you can focus primarily on your sleeping position to determine ideal firmness. A medium (6) or medium-firm (7) mattress suits most people in this category, though side sleepers may prefer something slightly softer.
Heavier Sleepers (Over 100kg)
If you weigh over 100kg, prioritise firmer mattresses (7-8 on the scale) with robust support cores. Softer mattresses will compress excessively, leading to poor spinal alignment and premature sagging. Look for mattresses specifically designed for heavier individuals, featuring high-density foams or reinforced coil systems that maintain support under greater pressure.
As a general rule, add 1-2 firmness points to standard recommendations if you're over 100kg, and subtract 1-2 points if you're under 60kg. This adjustment accounts for how your body interacts with mattress materials.
Sleeping Position and Firmness
Your primary sleeping position determines where your body needs the most pressure relief and support. Each position has different requirements for maintaining healthy spinal alignment throughout the night.
Side Sleepers
Side sleeping is the most common position, and it requires the most pressure relief. When you sleep on your side, your shoulders and hips bear the most weight and need to sink into the mattress to prevent pressure points. If your mattress is too firm, you'll experience discomfort in these areas and potentially develop pain over time.
Recommended firmness for side sleepers: 4-6 (soft to medium)
Back Sleepers
Back sleepers need a mattress that supports the natural S-curve of the spine. The lumbar region (lower back) should receive adequate support to prevent it from sinking too deeply, while the mattress should still contour to the body's natural curves. A medium to medium-firm mattress typically achieves this balance.
Recommended firmness for back sleepers: 5-7 (medium to medium-firm)
Stomach Sleepers
Stomach sleeping puts the most stress on the lower back, as the pelvis tends to sink into softer mattresses, creating an unhealthy arch. Stomach sleepers need firmer support to keep the spine neutral and prevent lower back strain. This is particularly important for heavier individuals who may sink even more deeply.
Recommended firmness for stomach sleepers: 6-8 (medium-firm to firm)
Combination Sleepers
If you regularly change positions throughout the night, you need a versatile mattress that accommodates multiple sleeping styles. A medium (6) firmness level typically offers the best compromise, providing adequate pressure relief for side sleeping while maintaining enough support for back and stomach positions.
Consider your dominant sleeping position—the one you spend the most time in and typically wake up in. Optimise your mattress choice for this position, even if you occasionally shift to others during the night.
Personal Preference and Health Conditions
Beyond body weight and sleeping position, personal preference plays a significant role in firmness satisfaction. Some people simply prefer the feeling of sinking into a plush surface, while others like feeling more "on top" of their mattress with a firmer feel.
Certain health conditions also influence ideal firmness:
- Back pain: Medium-firm mattresses (6-7) are generally recommended by healthcare professionals, as they provide support while allowing some contouring
- Hip or shoulder pain: Softer mattresses (4-6) offer better pressure relief for these sensitive areas
- Arthritis: Medium to medium-soft mattresses help cushion joints without sacrificing support
- Fibromyalgia: Pressure-relieving memory foam in medium-soft configurations often provides relief
Testing Your Firmness Choice
The best way to confirm your firmness choice is to take advantage of sleep trials offered by most Australian mattress brands. These typically range from 100 to 120 nights, giving you ample time to adjust to your new mattress and assess whether the firmness level is right for you.
During your trial period, pay attention to:
- How you feel when waking up—refreshed or achy?
- Whether you're tossing and turning more than usual
- Any new pain or discomfort that develops
- How the mattress feels after the initial break-in period (usually 2-4 weeks)
Remember that it takes time for your body to adjust to a new mattress. Give yourself at least three weeks before making a final judgement on firmness suitability.
Final Recommendations
Choosing the right firmness comes down to understanding how your body weight, sleeping position, and personal preferences interact. Use the guidelines above as a starting point, but don't be afraid to trust your instincts. If something feels wrong after an adequate adjustment period, most brands offer firmness exchanges or full refunds.
When in doubt, medium (6) firmness is the safest choice for most people. It provides a balanced feel that accommodates various sleeping positions and body types. From there, you can adjust firmer or softer based on your specific needs and preferences.