Back hurting from bed in travel trailer - need advice please

I've always agreed with folks that say you spend thousands of dollars on a TT,RV or %er and they give you a bag of straw for a mattress.
I've bought custom ones and mostly of late the Jayco folks have allowed for a residential one which works for us a we by one of the ones like at home. The biggest difference is the height our mattress must be 40% taller than what they give you.