Through trial and error, after buying a $$$ Sterns&Foster pillowtop that developed indentations after a week (and I needed something for my back problems) I did some research and decided to follow the advice I'd read. I exchanged the pillowtop for a Kingsdown extra firm mattress, then softened it with a mattress topper. It's been seven years. The mattress has no sagging or divots. I do have to sometimes rearrange the topper and have bought a few different ones, working with them until I found the right configuration. I"ve been very happy with this and just can just advise everyone to never buy a pillow top. No matter how much the mattress costs, the topping is the cheapest foam that will compress nearly immediately.