I don't really know how to approach this. You mentioned your weight like it was the reason why your seats are wearing, and it seems like you're trying to get them to cover it under warranty. Is Toyota's warranty different than Subaru's? Because as far as I know, seats aren't including in the wear warranty, and it also doesn't qualify as a defective part. If the seats were like that when you got the car, then they probably would've covered the upholstery job. I don't want to doubt you, but you're making it seem like the seats were fine before, and something you did made them start to wear and fade.
Try what @
humfrz suggested but you'll most likely have to spend money either repairing it or swapping the seats altogether.