With small door openings, high bolsters, in my case short legs and numerous old injuries, I still do my best put as little weight on the bolsters when getting in and out and have reminded my wife a few times as well. I still might end up with some damage over time but 20k miles is pretty early no matter how you get in and out of the car.
Consider this, do you want a mechanic, paid by the job, not an automotive upholstery expert swapping out your seat covers?
I know how to upholster and know it is not that easy a job, just taking the seats out and putting back in place it is very easy to damage the car, takes care to line up everything right so no ripples when done or soon after and the crack may be back in another 20k miles.
If you can just get them to supply the cover perhaps you can have a real shop out it on or store it until the wear is to bad, selling the car, etc.....