I can recommend "Heir to the Triple Throne" by Janus Rain.
https://www.smashwords.com/books/view/640330"Since she was a young girl, Adrienne hated her breasts. They were ugly, flat things, which she had been raised to resent, given her unique genetic defect and appearance. But, when her company makes her an insane, first-of-its-kind offer, Adrienne finds herself agreeing to throw all that aside to grow them to impossible proportions!"
It worked for me because the growth was realistic - Adrienne had to deal with the increasing weight of her breasts, and how difficult it is to move around. There's not much in the way of eroticism - don't expect hot and steamy sex scenes. Expect a woman constantly wondering just what the heck she got herself into as she needs more and more help dealing with her breasts....