After leather, automotive grade vinyl or marine grade vinyl would be the most durable. Don't buy closeouts for $8 or $10 a yard. Also, don't buy closeouts of leather, you never know what you're getting.
If you are not sewing the fabric to sew foam, (in other words, just sewing two or three layers of fabric together) you could use a home sewing machine to sew seat covers. You would need the largest needle the machine could handle, and use at least size 69 nylon or polyester thread. They are both equally strong, but polyester's color won't fade like nylon can. Otherwise, you would need an industrial sewing machine to do seat covers.
No one lives forever, the trick is creating something that will.