A picture is worth a thousand words, and a great night's sleep is worth even more. Most of us sleep on our sides, and when a latex mattress is properly configured, there is just the right amount contouring and conforming at the shoulders and hips to perfectly align your spine.
Now, it someone is 30 or more pounds heavier and was photographed on this same mattress sleeping on their side, you would see a lack of support at the shoulders and hips, and a spine that is not aligned, which will eventually led to lower back pain.
As well as size and weight variations for side sleepers, other firmness factors to consider are back sleepers, who do not need the same amount of conforming as side sleepers, and, finally, personal preferences for the overall feel of the mattress. All that being said, latex mattresses offer incredible support without the unnecessary firmness found in inner-spring mattresses.