@Maldon welcome to you!
In 2011 I had radiation treatment, I didn't have a lump at all, I had DCIS and went onto Tamoxifen for 4yrs. I did unfortunately have a recurrence 2015. My lumpectomy was breast conserving as am big breasted, clear margins. My recurrence was 2.5cm IDC Stage 2 Grade 3 aggressive, so I had to have chemo, no radiation as cant have it twice and another lumpectomy. A year after finishing I had a single mastectomy/diep flap reconstruction at their recommendation to avoid another recurrence.
The thing is, its not about how big your lump is, what's important is the pathology. Depending on that determines whether it's aggressive or not, early or later stage. No way of knowing without those results.
Not everyone requires radiation or chemo, some just surgery, lumpectomy or mastectomy. Try and hang in there, theres no way to speculate, once you have it all together you will have a very informed decision.
Melinda xo