BRCA2 prophylactic double mastectomy with reconstruction - should I get a fat transfer?

Unfortunately, without an examination in person, or photographs at the very least, it is difficult to provide you with an adequate response to you question. Fat grafting can be an excellent supplement to an implant based breast reconstruction or to an autologous (your own tissue) reconstruction, but rarely can it be relied upon exclusively to achieve an adequate breast volume. An “unnatural” appearance to your breasts may also be a function of implant selection.

I would discuss your concerns with your plastic surgeon, or consider a second opinion with an experienced board certified plastic surgeon whose results appeal to you. Best of luck to you.