I was directed to M&S as well.
I had to have a bra suitable for a mastectomy with immediate implant.
I found the asststant I asked (while sobbing) was lovely, knew exactly what my needs were and what was required with the op. She said she deals with fitting like this nearly everyday.
I have 2 full cup, total support bras which are lovely and soft - satin around the base and no seams anywhere. I was also advised to get extensions (also M&S) to cope with the swelling, that can slowly be removed as I shrink back to normal.
Still waiting for that moment though!!
I was very lucky, the assistant at my local M&S was the soul of kindness and tact. She helped me find a very comfortable bra, even though the one she wanted to offer was not in stock in the right size. She also helped me order additional ones to pick up at the local M&S food outlet.
Thank you for this post - I am really struggling with this at the moment and will definitely look for those.