replace the springs and foam if needed. One can also clamp the springs together with seat spring clamps.
Are the springs close enough together to use hog rings to tie them to each other? I haven't looked at the underside of seats in many years.
Someone will have to define "old", The seat springs I've had apart from the 80s - the early 00s are not close enough together to tie them together. Most of the modern seats just have spring steel straight wires running front to rear tied to an end bar they loop onto to form a wire spring steel weave sort of thing Then the seat foam may, or may not be bonded (but some just sit on top of the weave) to the spring wire weave assembly and fits snuggly into the seat frame. That seat frame breaks a lot, I've welded hundreds of them back together. Pill the cover, pull disconnect the spring weave from the seat frame and remove the foam and weld them back together. Reassemble in the reverse order.