I had a mastectomy in December 2007. Its not too bad really, just a relief to get rid of the cancer. There are many options for plastic surgery if the loss of a breast is difficult for you but it is more important that you get well again. My daughters' responses to my cancer and mastectomy were: "Don't worry mum, you don't need it [the breast] any more" and "You look much thinner without that breast, you should get the other one off".
Did you know that there is an 84% survival rate from early breast cancer these days - even though the words invasive/infiltrating cancer sound scary, this is still just early cancer! Isn't that fantastic! Do you have to have any adjuvant therapy? I have just finished a four cycle course of chemotherapy. This was pretty awful but not as bad as I had expected thanks to advances in the drugs treating the side effects of chemo. If you have a mastectomy you may not need to have radiotherapy, which is another good thing although, of course, it is better to have all the treatments offered to you to maximise you chances of living a long and healthy life after this.