I have a bad back, so I need a firm mattress. But sleeping on it causes fairly severe pain in all the pressure points (ribs, shoulders, hips, back). I tried putting a softer mattress pad on top, but then it doesn't support my back properly. This has been a problem for years, and appears to be growing worse as I get older (now 56). What would cause such severe sensitivity to pressure and/or what kind of doctor should I see about the problem? Thank you.