I just bought my Tacoma a couple months ago, and I've already got a couple small scuffs on the interior from my dog's toenails. I don't have seat covers yet, but even with those on, she could still dig into them. She doesn't deliberately try to damage anything, but she can't help but sometimes scratch up what she's on.
So I went to the craft store and rummaged through the discounted scrap fabric pile until I found a yard of grey vinyl. Perfect - it's durable, waterproof, and matches the interior.
The seat pad has been sewn with a couple layers of batting on the inside to give it some cushion. The front flap velcros down onto those metal hinges under the front of the seat, and there is a cutout for the seatbelts. The seat pad tucks in between the cushions and so far hasn't budged. It is also easy to remove to access the under-seat storage compartments.
I'm not a great at sewing and the thick vinyl broke at least one needle on the machine in the process, so it looks like a drunk stitched it.

I recommend using contact cement for the next person who tries it.
Then I made a cover for the inside of the door. Tanner likes to place her paws on the door to look out the window.
The door panel has cutouts for the window and handle, and it is attached by sticky-back velcro placed strategically on the plastic door panels. That way I can easily remove it to clean it.
The vinyl, velcro and batting cost me around $15.