I just bought a feather bed (which goes on top of reg mattress) and it was under $100 for queen size. Best purchase ever, really helps with sleep. Others have used a fiber bed because it is washable but I put mine on top of mattress then covered with fitted mattress protector then my bedding so I don't have to worry about that.
These are not mattress covers, but are thick pads that you put on top of your mattress, but under the sheets to provide a softer more comfortable place to sleep. They come in all bed sizes and can be cotton fiber or feather, or foam. I got the cotton fiber one because of my allergies. It is very hard to wash them because of their bulk, but most come with covers that can be removed and washed.
I got mine through a jc Pennsy's store, but they are availiable at amazon online and walmart stores. Just be sure it is thick enough to provide you will extra padding so that you can sleep better. Hope this answers your question.
Thanks Tina I have seen prices over $300 for memory foam but I would like something more natural and your's sounds like a good price range. I saw some for $50 and under but they looked like they were from old war movies!