We have a 1993 mh which we purchased just a few months ago. We also had a queen mattress that was in bad shape. In looking into how to get the darn thing into the bed room i called Camperworld to see what they had to say.
Camping world sells a mattress in a box that works much like the "TRANSFORMER" toys that were popular a few years ago. We bought the queen. It comes in a box that is about 5ft long and 1 1/2 feet square. You carry the entire box into the bed room, and there open it up. When you remove the plastic wrapping - stand back. It unfolds and begins to grow. Once it is all unfolded it requires 24 hours to reach full size.
This thing cost a bit over $400 and includes the pillow top. It is firm, and extremely comfortable. They come in a short queen, queen, full, and twin. I assume they also have a king.