We bought a new TT last winter. The first thing I did was give the stock queen-size mattress to Habitat for Humanity and replaced it with a Serta EuroTop from Sam's Club.
=. Sam's Club prices are about half what a discount mattress store charges for a similar nattress.
I did the same thing 12 years earlier for the mattress in our 5er. It was a bear of a job to get the stiff mattress up into the bedroom on the 25' 5er, but we persevered.
We just returned from a 4,000-mile RVing round trip from west Texas to eastern Tennessee, southern Ontario near Detroit, and northwestern Michigan (Sleeping Bear Dunes National Lakeshore). The EuroTop mattress was wonderful for two old folks.