We found the stock mattresses in our popup far too firm. After determining that there was a little room to spare between the mattress and the roof when closed, we purchased a 1.5" thick memory foam mattress topper from our local Target. Their 1.5" only came in a queen, so that's what we got. Made in USA, and despite horror stories of chemical smells, etc on these things, this one had none and seems like a great value.

Queen size is a bit too small for the nearly-king bed in the camper, so we plan to buy a 2" version in a king size and trim it. We'll move the current one to the smaller bunk for the kids to enjoy.

That said, even the 1.5" made an extreme difference in the comfort of the bed. Neither of us want to get out of bed now, and I no longer wake up sore like I did before we added the topper.