When I saw the title of this I was just about to say something about perfectionism (I also have an eating disorder) but I see you beat me to it...

You see the problem: I MUST (perfectly) overcome my perfectionism. I ABSOLUTELY CANNOT FAIL in being more relaxed. I HAVE TO get better.

I think with wellness--and the reason it is so difficult to obtain--is that you simply cannot focus on it with your eating disorder mind and hope to achieve it; you must look at it with a mind completely foreign to the one you currently know. Willpower in itself isn't bad, and it is certainly necessary, but how you respond to your mistakes (since you will certainly have mistakes along the way) will determine your success.