I've upholstered a number of seats, only because it was way too much $ to pay someone.
Get hog rings and pliers, they are inexpensive and worth every penny.
I went to a craft store, bought a 3" roll of burlap as well as larger burlap, iirc 3 feet wide.
The 3" roll was much stronger, and I stretched it both ways across the seat a few times, then covered it in the large burlap.
One seat I did the bottom foam was shaped from the factory, so I added a small layer of new foam under it, 1/4" iirc.
Wrap that in the sheet like stuff, muslin.
Setting covers in the sun helps, but I also put the seats face down on a table, placed a long board over it, and clamped it with wood clamps, board to underside of table, moving them around as needed while I placed the hog rings.
This made it much easier, less pulling and stretching the covers by hand while trying to attach hog rings.
Use everything original you can, for example any seat kit will have cardboard strands for the edge inserts, factory used metal wire, which was sometimes a wavy wire, not straight.
