As Louie says its a very personal choice to make and very hard. I spent a long time trying to come to my decision but in the end it was 'piece of mind' for me too to have both breasts removed. I couldn't stand the thought of going through this all over again. The medical profession are of the opinion that having a prophylactic mastectomy isn't necessary though they are supporting women who want it for the most part. My surgeon was reluctant at first but respected my decision. He made sure I knew what I was in for both physically and psychologically and I think that is really important. You may want to see a psychologist to talk things through. I found it helpful.
I wish you all the best for your surgery and I hope you don't have too hard a time in your decision.
Love and hugs
Janey xxx