I had similar choices and I went with the lumpectomy. My (Harvard Medical School professor) surgeon explained to me, and I researched, that the type of surgery I chose wouldn't determine whether I'd live or die from this disease.
There were other reasons, too - I was working and had to figure in all the time off I was taking, I had two young children, risks of more involved surgery, etc. But it's been a good choice for me. My original cancer, they say, is gone and likely won't recur now (after 15 yrs); my risks of getting another cancer are the same as anyone else's. Should that occur then I'll have more choices to make.
I was reading an article recently about the "Angelina Jolie effect" which basically stated that they are probably doing more double mastectomies now than are needed as people think it's going to be "better". But one really needs to do a lot of research for themselves to figure out exactly what the actual statistics say, and then decide what works best for them. Last I read, which was about several months ago, lumpectomy had similar survival rates to mastectomy for certain/many cancers and situations. If it's given as an option, than it's a good one to think about.
ETA people should also understand that recurrences can happen even with mastectomy because breast tissue extends down to under the arm and above the clavicle in some cases, so it's impossible to remove all of it. One of our posters here, Feralpeg, had cancer in her surgical mastectomy scar.
I am replying to this post above, but I'm also saying this for the people reading here. Knowledge is power, and it's good to have all the facts.