Agreed. You're going to need to get some more exposure to the floor pans to get the big picture on the total extent of the damage (i.e., pull the quarter trim panels and anything else in the area - which will also protect those pieces from collateral damage while you're repairing the rust damage).
Mine actually required replacement of the sheet metal floor pieces above the torque box extending to under the back seat. The vendor I purchased those pieces from no longer make them, but the earlier model years have the same pieces that would with some modification.
Here's the same area of mine with the new pans tacked in. You can see the "intermediate" panel on the passenger side under where the seat cushion would go. Also had to fabricate some pieces to go over the torque boxes.
QCode351Mach (Scott) has some awesome videos on how to replace the floor pans - it would be a good idea to check those out.
Hopefully, you're only looking at cleaning up/patching the inner rockers and dropping in some new floor pans - not too tough at all. ::thumb::
Getting a useable set of fastback seat platforms (if yours are no good, that is) will be the tough part. Be as careful as you can about getting those apart from the floor pans/inner rockers/transmission tunnel as you can if they're at all useable.
Good luck with it, and keep the pics coming. ::thumb::