I have skinny legs also but my boobs aren't big either. I'm a B cup. Yes, 5'5" and 123 is on the thin side. Well big boobs can cause back pain and reductions are covered usually by insurance. I would do that if I were you but you have a lot of health issues so a needless surgery might not be ideal.
I know my bmi but i am too embarrassed to put it on line. I have, however, brout it down by losing 50 pounds. I will continue to loose some moe weight and bring it down further.