We have a latex foam mattress with a memory foam topper. We replaced an old topper with the new one. It fit perfectly and made an outstanding mattress that we love. I think it was the 5 lb feature because the old memory was only 3 lb. We never slept better.
Very disappointed, considering the high price for this. It's ANYTHING but firm. Bought because of "5-pound density" of foam. If accurate, that is nowhere near enough to constitute "firm." The foam's also ripped in a couple of spots, on the side where I get into bed. I've had this a little over a month.