I've been taking hormones for 4 years, and I live as androgynous. The hormones can help a lot if you are trying to be androgynous and have a feminine look at the same time, but again, they may have some unwanted changes. Obviously, you will probably develop breasts. However, if you are very thin, then you may not develop a noticeable amount.
Also, you can try running, cycling, elliptical and so forth to burn calories and fat, this way it is harder for your body to start growing breasts without an excess supply of fat and calories. If you are very thin, and exercise, then you should get minimal growth. As I stated, I've been on hormones for 4 years, am very thin and exercise frequently, and I am still flat chested. Also, running and other leg exercises are good anyway because they will build your legs and butt up and give you a more feminine look.
