I am so sorry your mother passed from ovarian cancer, it is horrible - is that why you had BSO? Are you a BRCA carrier?
I am a non carrier within a BRCA2 family so it is something I have had close contact with too, and lived in terror of it myself until I got risk reducing mastectomies at 29 and then genetic testing at 34 showing I was negative.
Perhaps irrationally, I was always much more frightened of breast than ovarian as most of my rels with breast were young, whereas the one aunt with ovarian was old, and also I could see my breasts, and was always scared of feeling a lump - I used to use a sponge to wash so I didn't have to touch them! But ovarian is far less treatable and often diagnosed too late.
I am surprised they left your uterus when you were having this surgery anyway, committing you to potentially long term progestogen use should you choose to take estrogen. It was known well over 5 years ago that it is the progestogen that confers the breast risk.
Regarding the cancer risk, you no longer have ovaries and combined continuous MHT confers a LOWER risk of endometrial and colorectal cancers than untreated women have.
Breast cancer - worst case scenario there is a SMALL increased risk with combined MHT in general. This cannot be extrapolated to BRCA carriers who have a high risk anyway and there is not currently any evidence that hormone therapy further increases breast cancer risk in this population.
It does add an extra layer to the decision making process, but to put it in perspective far more women suffer and die from cardiovascular disease and osteoporosis than any type of cancer, and you are already in an advantageous position not still having your ovaries at least.
I think in your shoes if breast cancer is still a concern I would probably go for Tibolone. I may also choose this myself when the time comes to switch from the COCP which I have been on since right after my risk reducing surgery, primarily to halve my risk of ovarian but for other quality of life benefits too.