Best thing we ever did was to get a van with a fixed bed. No more humping and lumping cushions around at a late hour and having to do it all again in reverse in the morning! We make our fixed bed up before we leave to go on a trip and use cotton sheets with a duvet, which is much nicer than using sleeping bags.
If you find your mattress too firm, there are memory foam toppers to give you a comfortable nights sleep. The best ones advertise in the caravan magazines and use top quality foam, cut to fit over your mattress if you tell them the make and model of your caravan.
Happy and safe caravanning to you!