First, a couple of practical things: I urge you to invest in a good heavy-duty office chair. If you get a chance, try an Aeron C — I had one that lasted me eight years and someone else is still using it. They don’t make them any more but you can find them on eBay etc. I also urge you to go ahead and use the ADA desk if you need it and no one else does. I’ve heard from other fats that the Kia Soul is reasonably butt-friendly — I gave up my car but my city does not have good bus service so I use Lyft.
You belong in the world, even if you sometimes have to speak up for your right to be here. I find it works best to assume the attitude that I have a perfect right to be where I am.