That sucks, what a hard choice :(
Only you know how you will feel about losing a breast - if I had needed to make that choice I would have in a blink. And like Afrasa I wouldn't have bothered with recon, prosthetics are so good these days.
I was also Her2+ but only a small tumour so a wide excision, chemo (yay, that was fun ) and radiation fixed me. Well, we are never actually completely fixed are we, it can come back to bite us at any time.
The best soltuion is the one that leaves YOU feeling that you have done everything you can to beat this, with advice from docs, oncs and surgeons. Some people think surgeons have no empathy, but mine was the nicest person. Be advised by them, they will only suggest what they think is the best.
Take special care <3