If you're unsure, it's imperative that you try out some mattresses so you can get an idea of what's the best mattress for you. Generally, back sleepers and those who are of a heavier stature are best suited to what an extra firm mattress can supply. For heavier people, the stronger and firmer springs mean they can fully support you weight, evenly distribute it and ensure that the spine is properly aligned. For back sleepers, it's important that the middle of the back doesn't sink into the mattress to avoid causing back pain and aches, which is why a firmer mattresses are seen as being more appropriate.

For side sleepers, you're more advised to get a softer mattress. This provides more cushioning around the shoulders and hips, which in turn helps properly align the spine. Front sleepers, although the position itself puts added pressure on your spine and neck, are best to sleep on firmer mattresses. Although you can wake up with aches and pains simply from sleeping this way, your spine will be most supported when on a firmer mattress. Having said this, an extra firm mattress may be too much for a front sleeper.