Mattresses are by in large a racket. Ever wonder why there are so many mattress stores around? Because the markup on them is massive. Get a decent foam one from Costco and Amazon and you'll be way ahead.
I think the one we put in the camper cost around $200 on Amazon and it's great. It is a little heavy which can make the storage access underneath a little annoying but no big deal. I might spend a bit more on one for the house but not more than about twice that. Any more is a waste of money, imo.