I regret not having a double mx. I am very overweight and so they removed over 600g from one breast. One reason for no mx (I had said I would be happy to have one) was my weight - it would have made me even more lopsided, but the other, I think, was that hospitals here in Germany are sometimes judged on the number of mxs they avoid.
Anyway, I had a lot of radiotherapy and as a result I got lymphoedema in the breast and trunk. It took me a long time to get used to the fact that I will need treatment for life. My tumours were not large, but multiple, hence the biggish operation. It's 5 years on now and I still have trouble with the breast. I can't help feeling this could have been avoided if I hadn't needed that radiotherapym, although of course I don't know what lymph problems I might have got with an mx.
The weighted prosthesis I eventually got (after 3 years) makes the lymphoedema worse. Wearing a bit of 'spaghetti' - a sort of foam sheet with ridges in it - helps a lot, but there's no way I could wear a prosthesis on top of it.