I had an old mattress that I squeezed an extra year out of by putting a thick memory foam pad on. Costco sells an awesome one. I loved it so much that when I did buy a new mattress I couldn't sleep without it. So I bought another foam (different size mattress) but then I couldn't climb into bed or put any sheets on because it was so high. LOL

Why do you want another full? Queens are like five bucks more! New bedding would be an added expense but I think it's worth the investment.