I am heavy - about 250# - and need a mattress that will hold up and help with back problems. My doc says one of the reasons I have trouble losing weight is that I don't get a good night's sleep - I have fibromyalgia and back problems, among other things.  So I'd like to replace my mattress with one that will not only hold me comfortably, but hold up so I don't have to replace it too often (I'm on disability and can't afford that!) and is not too expensive for my limited budget.  I've been considering Tempurpedic - I've heard it's great for fibromyalgia but want to know if it can handle my current weight.  I've also looked into wool but it looks beyond my means.  Any suggestions or thoughts?