Orthopaedic mattresses - please advise!

Suzemac

Hi, our family are relatively new caravanners and are planning a trip to France this summer.  However, I've had a few problems with my back and am worried that the long journey coupled with sleeping on a made-up caravan bed, may cause it to seize up competely! 
I wondered about getting a more supportive mattress - has anyone done this for a tourer?  Had a look at some websites but got competely confused (not difficult for me).  Thanks for any advice.