Whatever you choose will be right for you, imo, since you are considering it so deeply.

IMO you shouldn't get one at all at this time. Eating disorders are a form of self abuse, and in this instance I personally think the tattoo is also a form of self harming.

You could have wash off ones made of Stay Strong for yourself... or have one of those colored rubber wrist bands made up for one... it would give you the same encouragement without "harming" or disfiguring your beautiful body. Just my POV and something to think about?