Just to piggyback on this I'd love if folks would assume that, as a man who has been both fat and disabled for decades, I am familiar with literally everything you're going to say is the "simple" thing that would "fix" me.
Nine times out of ten, I'm already doing it, and still fat. Still disabled.
My mom once complained that her leg cramps were worse than usual, and I said potassium supplements had been helpful for me, and she said "oh it's spinal stenosis, and also I drink orange juice every morning" and I felt about two inches tall.
If any of it was simple or easy enough for me to do, I would already be doing it. I go for a couple of short walks every day when I can't do long walks. I don't allow myself to collapse into eating disorder mode when I feel guilty about my body. I try to drink lots of water and rest when I hurt.