Hi Jill - Our post on dressing after a mastectomy will give you some good tips on how to go about selecting a bra, and how to get it fitted. Best of luck to you - PJH
Jill, why don't you try a large department store with a person who can measure you and help you find a good style? Another option is to check with a shop that fits prostheses for mastectomy patients. They will have small "fill-in" gel pads designed for lumpectomy patients that may help as well. Insurance may cover the cost if you need a filler, but if you want to file for insurance, you will need a doctor's prescription.
You are probably measuring one size, but may need a larger cup size. I had a unilateral mastectomy and then an augmentation on the other side. I measure a 34 C, but that bra size doesn't fit right. Here is a website that tells how to measure with implants. It seems pretty accurate. You may have to try on different sizes and styles to find what fits right. Good Luck. Here is a link to the website. It tells you to measure each breast individually and how that translates into cup size.
Best of luck and although it can be frustrating, you'll love it when you find a bra that fits right.