Personally, I believe that if one has a healthy spine, a mattress is not a serious issue. After healing from ADR in 2004, I never really gave the idea of bedding much thought.
Unfortunately, some people will have to "invest" in some more expensive mattress solutions, which seem to help many patients get more restful sleep. Here are some past discussions on "getting comfy" at night:
Bed Mattress: Tempur-Pedic vs Sealy True-Form vs Sealy Posturpedic Plush, etc.
New Bed, better sleep, and...
Temperpedic on the way
Searching for New Bed
A word about 'tempurpedic'
Mattress suggestions?