Fat transfer is a great way to augment since you are using your own genetic tissue instead of an implant.
LordKAT and FrancisAnn are right about holding out. You should wait until you've been on E long enough for breasts to develop however they will. I've seen people say you should wait 1-3 years. Some people even get a little bit more breast growth as time goes on / after srs or orchi.
Fat transfer is great, though, if you have enough fat to harvest.