I fixed the couch in my basement with a scrap piece of 1/8" aluminum sheet, an old beach towel, and a coconut. The front support (extends from left side to right side of the couch, supports front end of the seat) had come loose on one side. It was a cheap couch, made with what looks like particle board so nailing/screwing it back together wasn't gonna happen. I unscrewed the leg on the offending side just enough to support part of the aluminum sheet, the rest of the sheeet supports the front end of the couch.
The beach towel adds a little more support to the seat where the original supports had stretched out a bit (straps and thin foam, no springs, nothing substantial to hold up my fat ass).
The coconut (two of them actually) also help hold the front end of the couch. It wasn't built beefy enough to only have 4 legs, needed a middle support. The coconuts were the only thing I had handy.
That was about 2-3 yrs ago, everything is still holding up well
