Hi Janet
Perfectly understandable to be concerned but if you have your health professionals encouraging you to start Tamoxifen I would do so. Their job is to look at your pathology results and go with the treatment guidelines that are recommended to them based on research. Right now, your pathology results suggest to your surgeon and oncologist that tamoxifen will be a good choice for you.
When you look at that 10% number, it is not telling you the whole story. When you try and weigh up the advantages and disadvantages we overweight short term advantages (not taking meds) over fuzzy but important long term advantages (better health/life outcomes). This is why I go with professional advice over trying to "game" the system.
I have a friend who was diagnosed with cancer which was low hormone sensitive but she is on Tamoxifen, caring for a family, setting up a business and running a cancer support group while getting back into running.
So many people are on Tamoxifen and find that the side effects are not noticeable especially if they keep active. I'm one.
Keep talking to your breast care nurse and hang out with breast cancer support groups where you can share with fellow survivors IRL. You'll be surprised at the range of stories, good and bad, but on the whole, pretty good.
Love and hugs