Most ladies here report that at 3 to 5 years of HRT your breasts will be about as big as they will ever get by hormone therapy alone. If you still want to be bigger, then surgery is one option, not the only option.
I have one friend who tried Estradiol and mentally, it just did not work for her. So without much of any HRT she had a BA with 600 cc silicone over the muscle implants. She still wants to go larger.
Of course, you can get a BA at any time you wish.