Hi there
This is such a personal decision!
in my case my first consult with my breast cancer surgeon he talked about my options of a lumpectomy or mastectomy.
At that stage it appeared I had a 4.5 cm lobular cancer and I had big breasts ( E cup).
Further tests showed it was in fact 5.5 cm.
My surgeon still said it was my choice but if he did a lumpectomy it might not get clear margins and I might then need a mastectomy anyway.
I decided to get the mastectomy and then actually got the other one done and had DIEP flap reconstruction.
I am 63.
Even though it is an intensely personal decision your medical team can help you with the pros and cons.
For example in your case, the size of the tumour is small and now you will be part of a more intensive scanning regime so if there is another cancer in that or the other breast it should be caught early.
In my case , part of my reason in getting the double mastectomy was that my breasts were dense and my cancer was not picked up on a mammogram so I was very wary of the screening technology picking up another one.
All the best with whatever you decide.
if you go to the mastectomy route it would be worth joining the “choosing breast reconstruction” private group on here.I found it really helpful .