A self tapper will just vibrate and walk out. Buy a nut cert kit. Drill the correct size hole for the cert, you will install a threaded insert with the tool, and can install a bolt to do the repair CORRECTLY !!!!
The new foam is far superior than anything you have that is 25 years old. Secondly I replaced the seat bottom in my 1999 k2500 suburban, gray cloth, and it matched 99% exact and that is all you can hope for. Again the material and the construction is way better than the stuff 25 years ago...
Check the drivers side switch and wiring in the door jam first. If there is a broken wire or a bad switch, the passenger side will be dead also. Check for power at the actuator while you have the drivers door panel off.