I have suffered from eating disorders for most of my life. When I have been really skinny, I had no boobs at all. I mean none. Now, I am doing better with the ED, and am a supposedly healthy weight. I am not very comfortable with my body, but I am thrilled to have some boobs!! So when that part of my head starts berating me for being too fat, I'll talk back to it and say 'well at least now I have breasts!'
I don't know what my bra size is because I never wear one. (I would guess I am a B cup?) When I was very thin and flat chested I never needed a bra. Now I probably "should" wear one, but I am not used to them and find them very uncomfortable. So, I still go without. If I feel I am too exposed in some of my clothing, I just wear a tank top underneath. Much more comfortable.