How to correct a sagging mattress?

Insert a piece of plywood between the mattress and spring. This should take care of some, if not all of the sag. Hope this helps.

Sagging Mattress

Mattress have a rather short life. There is not much you can do. Have you contacted your landlord about replacing a worn out mattress. I doubt that a tenants rights group would be much help in the matter. If he declines your option is to put up with it or leave. If for whatever reason you decide to stay a plywood board 3/8 or 1/2 inch thick between the mattress and box spring would help but not by much. Some lumber yards will trim a 4x8 foot sheet of plywood to your dimensions. Make it a couple of inches less than the mattress size.

I would make sure that the bed frame is not bent or missing a beam where the bed is sagging. That can be fixed. If it is the mattress itself, however, I suggest you to at least set that mattress aside and get at least an air mattress to hold you over, you don't want to hurt your back. I remember renting furnished houses and apartments, some of the beds I had to sleep on were brutal.

Try some large cardboard boxes in between and get a memory foam mattress pad for the top. The cardboard won't be as hard as the plywood so it will be more comfortable, the plywood will make the bed hard as a rock since the padding is obviously deteriorated.

ask your landlord to replace it. or place a 'stiffener' (board or hard plastic sheet) under your mattress on top of the box springs and get a foam mattress pad (the kind that looks like an egg crate works best) also turn the mattress over and you can even spin it end for end after flipping.

Try turning the mattress upside down and flip it over.

Otherwise the only thing to do is, ring the owner and find out if a new one can be arranged.

Have you flipped it upside down and spun it around - likely this should be done every time you change your sheets!

Hmmm if its really bad and you have to get a board under it - likely time to tell the landlord to replace it ;-)

Good luck

flip the mattress..get a mattress pad..