Hi, I also opted for a double mastectomy, as my first tumour didn't show up on a mammogram. I had 2 of them 3 months apart, and still it only showed on the ultrasound. I was always going to have trouble trusting a mammogram. I did have an MRI, which showed nothing else suspicious, so my surgeon suggested sorting out the cancer first and returning 6 months after chemo for the other one. I did that, and have had reconstruction with implants, and am very happy. I know I did the right thing for me, and I have no regrets.
Good luck with your decisions. Love Chris xx