There are differing opinions about this question with the breast cancer oncologists' community. There are some oncologists who think that HRT is safe for breast cancer survivors many years after the cancer but that is very much a minority opinion. It's one of those areas where there's insufficient research data to suggest that there is no risk, comparable to conflicting studies as to whether soy is a safe food for breast cancer survivors. There are no drugs, yet, for osteoporosis are without very significant side effects so I understand wanting to avoid them if at all possible but I'd be very wary of estrogen or estrogen-mimicking drugs or supplements if I'd had an estrogen-fed cancer in the past.

Maybe you can find an endocrinologist with significant experience in this area to discuss it with. I'd want a top-notch endocrinologist who isn't selling anything as the HRT world has its share of charlatans as part of the "aging well" supplement market. I have a healthy respect for master hormones so would do a lot of research before tweaking the balance.