Maybe we should have been stricter about allowing them on our bed at all. We should have been less tolerant of their little sophistries - "I'm not bouncing, I'm just walking" [in a bouncy way]. Letting them in there un-supervised with one of their bigger-boned school friends was the last straw.
So,
we have one ruined mattress. We have back-pain, we have grumpiness.
And yet, I don't want to throw it out and buy another. I'm going to, but I don't want to. What I want to do is install one of these...
<half-baked intermission> Elf Shirley on viola </hbi>
The collapse of the mattress is not complete, but is confined to a central band, stretching from side to side. The Anti-Mattress Under-Mounted Über-Spring approximately matches the concavity of the collapsed area with the convexity of a metal sheet underneath it.
This metal sheet is confined at the head and foot of the bed in two broad sets of jaws, made of thicker and more rigid metal. These two sets of jaws are mounted on big cog wheels, sitting on toothed racks, possibly scavenged from some vehicle's rack-and-pinion steering.
Long, detachable levers allow a team of two to push the 'foot' jaws closer to the 'head' jaws. This operation will make you look like a medieval torturer, except that you're pushing on a sheet of metal, not pulling on a person.
Under this pressure, the metal sheet starts to bulge upwards in the middle. If the bulge appears in the wrong place, you can guide it into the right place by confining it between rigid rods mounted across the bed frame between the mattress and the anti-mattress.
When the upwards bulge is about the right shape, you can lock it in place with vertical rods passing through the bed frame. Then, put the tired mattress back on top, and 'make the bed'.
Mind your fingers.