The mattress listed above is advertised as extra firm.I purchased this mattress because I need to sleep on my back on a very firm mattress due to two back surguries from previous injuries.I purchased the mattress on 10-1-2008 at the Mattress Wharehouse in Mechanicsburg Pa.While sleeping on this mattress I sink down about 4 inches, the bed sinks into a bowl with no back support at all.At 6foot 1 inch and 220 lbs I'm not obease.I have been experiencing lower back pain to a high level due to the failure of the product to live up to its advertised level.I want and need this mattress to be exchanged with one that does NOT sink into a bowl shaped depression.That is what I told the salesman I needed but that is not what I recieved.