About a month ago we purchased a new queen mattress for the camper. Got the same identical one purchased for our bedroom in the house, except the one in the house is a king size. We're hanging on to the factory installed mattress in the event we ever sell the camper, the original goes back in the camper and we're keeping the queen (for the next camper)(even though we do not have a queen bed anywhere in the house.
So, just purchase a mattress that you would purchase for your house and SLEEP COMFORTABLE! Don't cheat yourself! 1/3rd or more of your life is spent in bed. Why not make it the best money can buy. That's a lot of time in you're life you're spending flat on your back! Why not make it comfortable?