Understood. I had some reservations like this initially. However, mentally and emotionally, I could not look at one healthy breast with the thought of "what if it comes in the other breast then I am back under the knife again". I think it would have been very overwhelming. In doing the double mastectomy, that too assisted with that.
You are correct, you can be monitored and it is your decision. You must do what is best for you. In my journey, I find that this impacts each person differently. A lot of support groups, when they get to discussing chemo/radiation and medication...I cannot relate and look to find those most closely relating to my own journey. It's tough but you will get through this!