Hi Kay,
I've had a completely awesome experience with BAS, done by Meltzer back in the day.
They were done after 1.5 years of hormones, going from an A cup to a C cup. Nothing ostentatious, I wanted them to look as natural as possible. Well over a decade of HRT later (with a couple three years of being off HRT thrown in), cup size hasn't really changed other than through weight gain or loss.
I needed more breadth than anything else, because of the shape of my upper body. We went under the areolas, to help camouflage the scar, and they were placed completely under the muscle. The implants were Mentors, saline, round moderate profile, I want to say about 400cc, I think going closer to a nominal fill rather than a maximum fill to get that breadth without being too hard, but I might be misremembering that particular detail.
I found the pain of BAS (7.5 out of 10) to be more significant than SRS itself (6 out of 10) with facial surgery setting the standard of "10" for me on the pain scale. It was easily managed, though, with appropriate medication. Soreness lasted for about a month.
Everything was pretty hard the first weeks postop, due to swelling, and it took several months for them to settle. I had to massage them regularly to prevent capsular contraction. Not wearing a bra for years and years has helped to create some natural sag. Today they're pretty soft, but firm, and they jiggle nicely. The only tells are when I raise my arms over my head (my boobs rise up in unison) or if I flex my chest muscles (so I don't do that). Given my chest, they tend to spread apart, and only with a sports bra can I actually generate any appreciable cleavage.
There are several day-to-day ramifications that make a big difference to me. First, my whole upper body looks much more proportional and feminine now; I don't cringe when I see myself in the mirror after I step out of the shower, I can actually appreciate what I have. Second, I can actually find appropriately sized bras. Third, and most importantly, a much wider range of clothing now works for me. Finally, it made me much more attractive to men -- I started getting hit on much more frequently after I had this done.
I've had no loss of nipple sensation; the whole area has always been quite erogenous. I've had many lovers, and none have commented on my breasts being "fake" or asking if I've had my boobs done (though maybe I've just had wise lovers). Indeed, they tend to pay lavish attention to them, appreciating them greatly.
It's one of the best decisions I've ever made.