I bought the camper King size after trying out wilderness RVs firm hybrid for two months and this one just seems to hold up better. I was looking for the firmest hybrid out there and this one is it. I'm pretty sure if you belly flop on it you'll knock the wind out of yourself, and that's exactly what I was looking for. I'm sleeping on the extra firm side and after a month it's starting to loosen up a little and it's just right. So far I'm happy with the mattress and glad they took making a true firm mattress serious for those of us that need it. I have to sleep on my stomach, which can put an arch in my back if my lower back sinks in and cut off circulation, this mattress keeps me nice and level and on top of the mattress. Not knocking it at all, but if you sleep on your side, your hips will feel it for a little bit as it adjusts to the firmness.