Sorry to see you here.
All breast cancer diagnosis have different treatment plans. It all depends on the type of breast cancer you have - whether your 5mm lump is DCIS, locally invasive or Lobular etc, whether there is lymph node involvement, the hormone receptive status and so on.
Has your surgeon mentioned chemotherapy to you? If not, I would suggest waiting until you know what your treatment plan is before finding out best place to have chemotherapy. It also depends on where your oncologist is too.
My mother had a 19mm invasive but no lymph node involvement and she just needed a lumpectomy. She will be going on hormone treatment and is currently being assessed to see whether she’s suitable for a trial where she won’t have radiotherapy and they just monitor her For the next 10 years instead. She is 67.
Her close friend was diagnosed with DCIS which was something like 2mm in size. She had a lumpectomy and radiotherapy and that’s it. No further treatment.
I, on the otherhand had 22mm invasive, multifocal involvement (which means that I had cancer in other areas of the boob) and lymph node involvement so I had to undergo chemotherapy, radiotherapy and then had bilateral mastectomy plus hormone treatment. I will be having my ovaries removed next week. I’m now 42.
So you can see that different diagnosis have different treatment plans.
good luck.