I purchased the SertaPedic Sanborn Plush Twin mattress for my daughter for her first big kid bed. It was her favorite one in the store and when I laid down on it, it was so comfortable! It has just the right amount of softness but firm enough that you don’t sink too far into the mattress. It’s a substantial size (not thin) because we wanted something that seemed like it would last her years down the road. We bought another one for my son so now they have matching mattresses!