My TT came with heated mattress but you can buy heated pads from Amazon for ~ $60-$70.
If you have to settle for a regular queen size pad just let the extra 5" hang over the foot of the bed (difference between RV and Std Queen).
Electric blankets are good too and easier to find with dual controls if partner likes to be warmer or cooler.
A funny thought. Here we are talking about "camping" with electric mattress pads or Electric Blankets.
Remember the days when extra heat in you bed depended on who had the dog sleeping next to them in the tent?