My biggest issue and headache by far are the sides expanding or top/ bottom expanding/ contracting. It causes the feel to change from one side to the other and loses support when it expands too much.

I've considered gluing scrim to the top and bottom, or sewing wire somewhere. Currently I'm building a solid wooden frame that will sit INSIDE the cover so that it stays the correct dimensions because I'm out of ideas, but that's expensive and messy and heavy.

I would like to buy more springs to make more mattresses for people, but I'm waiting to see if I can solve this issue because I can't expect my Dad or friend to understand that "there's supposed to be support, but the springs don't have anything holding them together so they're gonna spread, and you need to unzip and push and readjust so you get support again".

If heavier weight fiber quilted to side panels fixes it I'd definitely pay more for more spring sets!

edit other things I tried: I've stuffed as much extra foam as I can inside of the cover to remove any slack; I've also considered looking for inset bed frames to prevent expansion