Hey TMM! Sorry to hear about your diagnosis. I don't check in here much (trying to get on with things???), but I did want to respond to you.
I had a double mastectomy in July 2014. Under regular old breast cancer circumstances i might not have but here's why I did:
1) I had a rare tumor that can come from intraductal papilomas. I had already had one papiloma removed form my non-cancer side ( and one form my cancer side) and had another one that needed to come out.
2) On my cancer side, I'd had a biggish papiloma removed in late 2013. If I did a lumpectomy and radiation, that side would have been way smaller than the other side (it was already smaller before all this).
3) My mother was going through cancer treatment, and I was driving back and forth every weekend and sometimes during the week taking care of her (150 miles RT form my house). I didn't have time to deal w/ six weeks of radiation treatments.
4) I was the third sibling in my family to be diagnosed w/ breast cancer (also have an aunt that had it), so even though my genetic testing came back negative, everyone says there has to be some genetic cause, so I didn't want to go through all this again.
5) If I had done just a lumpectomy, I would have had to do radiation, and if I later had to do mastectomy, it was only 50/50 that reconstruction would work.
6) Recovery from a double mastectomy was about the same as a single per my plastic surgeon and my breast surgeon.
Before you make your decision, you need to determine your risk for recurrence or a new primary cancer developing. Are they letting you talk to an oncologist before you decide? I know that's not always the case. I opted to do the genetic testing before my surgery, so that gave me some time. I met w/ the oncologist and plastic surgeon before I made my decision to get as much info as I could.
Please note that just because you have a mastectomy (single or double) that does not always affect whether or not you will need radiation or chemo. Luckily I needed neither. Nothing in the lymph nodes, tumor was right behind the nipple so not near the chest wall, the tumor was triple negative but low-grade (had it been high-grade they would try chemo even though my kind doesn't respond well to chemo; low grade doesn't spread very much so mastectomy pretty much takes care of it).
They did end up find ADH throughout my non-cancer breast that ahd not shown up on the mamograms, ultrasound or the MRI, so my oncologist said I made the right decision.
I don't know if any of this helps. Lots of good info on breastcancer.org. Just don't rush into your decision. As long as it's not inflammatory BC (my oldest sis had this, you can't wait on that kind), you have a little time to decide.