I agree, that stuff is way too thin to hold up on seats.
I ordered my interior supplies from Sunbelt Fabrics, Inc. located at 2506 Louise Ave. Dallas. Their Phones # are 214-421-9882 or 1800-322-8004, talk to Dean. They ship real fast also. He carries quite a lot of different vinyl (generic term) from different manufacturers and can advise you what works best for your application.
You won't have to pay sales tax either.