I'm not married and I have a bed all to myself but as a person with a bad back, I can completely relate to sleeping on an uncomfortable mattress. I just bought a new one in march and it has GREAT support. It has a combination of memory foam and coils and it is SO comfortable that I could stay in it all day
. When I visit my parents, I can certainly feel the difference and my sleep is much more restless since their mattress doesn't have as much support.
If I were married, I don't think I would feel ok with sleeping in separate beds. I would definitely get a mattress that supports my bad back and I would get one large enough so that there would be room for the 'kids' and the husband. I think it's a personal preference, though--whatever works for you and your husband