About 3 years ago I bought a Serta firm mattress. In less than 3 months there was an indentation - enough for me to get a replacement. (and I'm average weight for 5'4" female). That replacement mattress began to sag after a month. Got another replacement and that one did the same. (It's now in our guest room). Then I bought a Sleep by Numbers and have an aching back all the time. So I no longer truly believe in a mattress lasting for very long these days. I've done research online and have read that the all cotton mattresses last longer but are incredibly expensive. So right now I don't have much faith in the bedding industry and am leery of trying a new mattress...but my back needs some relief so who knows...