This mattress definitely won't substitute for an orthopaedic mattress. It is too soft if you have spinal stenosis or disc.problems. I was sleeping on a 20 year old orthopaedic firm mattress with a 3" memory foam topper prior to purchasing this mattress. It was still very comfortable but I thought it was past time to "upgrade". Bad mistake. This one kills my back. And, after 6 mos., it DOES sag on the edges when sitting on them. I weigh 228 lbs. for what it's worth.