What should I look for when mattress/box spring buying?

Question:Obviously, I'll lie down on them, but is there anything that's really important?

Also, do any websites describe the differences between all these types of mattresses? The stores have different names for the same/similar types to prevent you from cost-comparison shopping.

Thanks in advance.

Answers:
The minimal quality polyurethane foam used in the top layers of most innerspring mattresses rapidly degrades, resulting in body depressions. One option is to purchase a less expensive firm model and add your own 3" talalay latex topper and wool fleece pad.
http://www.memoryfoam.com/searchresults.
http://www.mattresspaddirect.com/...

Also consider a 6" firm talalay latex mattress.
http://www.foambymail.com/latexmattress.