Sorry to hear your oncologist didn't listen to your preferences. It's such a personal choice that I think we really have to be comfortable that we are doing the right thing for ourselves but of course it can be hard to argue against the authority of the medical profession. I think you're right in saying we should get a second opinion if we're not comfortable.
I was diagnosed in April 2012 at age 46. I had a 27mm estrogen and progesterone +ve tumor, stage 2, grade 3. plus some DCIS. I was offered the option of a mastectomy but the idea totally freaked me out to be honest so I just had the lump removed and a sentinal node biopsy. (No node involvement thank goodness). I had 4 rounds of chemo, then 6 weeks of radiation and I'm now on tamoxifen for another 4.5 years. My oncologist has suggested switching to an aromatase inhibitor (like aramidex) when my menopausal status is confirmed (haven't had a period since starting tamoxifen) but I'm reluctant to change because I've read that a lot of women have unpleasant side effects on them ie severe Hi joint pain and stiffness and no libido. Tamoxifen is interfering with my sleep a bit but apart from that I'm okay with it.
My breasts are now slightly uneven and I have seen a cosmetic surgeon about having the left breast (a D) reduced a little to match the right one which is probably a C now. I'm a public patient so who knows how long I will have to wait for that. But i suppose I'm lucky in that the difference isn't too noticable.
I hope you can get the result you want regarding your right breast. It seems a lot of women like yourself feel safer with a mastectomy. There are no easy answers with any of this stuff. Good luck.