Comparative mattress weight

I'm not quite sure where this should go, but General is a bit too general, so I'll try here.

I'm looking for a mattress that weighs as little as possible. I can't turn my mattress over, or even just turn it around, because it's so heavy.

We had a rubber mattress once, and it worked very well, once the rubber smell had worn off. After some 15 years we got a foam one, but it was a failure, because it simply flattened in between lumps. I think it was cheap and not well made, but we didn't realize that at the time.I now have an old regular (i.e. not rubber or foam) mattress and box spring set, but it too has become very uneven.

I need something I can turn over, etc. by myself., lightweight but resistant to getting all out of shape.