Our original mattress was horrible too. We replaced it with a custom-sized mattress from The Original Mattress Factory. They sized it exactly for our under-sized King; 74X72. An added benefit was the mattress is "hinged" so that it was easier to get into the trailer.
2018 F250 Lariat 6.2 4X4 w 4.30s, 2018 Wildcat 29RLX
2012 BMW G650GS, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
Jonsered 535, Can of WD-40, Duct Tape
Red Green coffee mugs