I think you would be better off covering the seat properly. The reason it is bouncy is that the fabric has broken down and don't hold it together as it was intended. Anything that you stuff into the springs is gonna break up and fail including tying the springs together.

1953 Chevrolet 3600
Fried Green T'mater (Vern)
In the Stovebolt Gallery
Caution: Political Statement
Man who runs in front of car gets tired, man who runs behind car gets exhausted.