I was diagnosed the same and opted for single mastectomy. I was assured by my surgeon from scans there was no node involvement. The doctor who did the breast biopsy before surgery also said the nodes were small and there was no need to do any lymph node biopsy.
The surgeon did the mastectomy and conservatively only took the dye highlighted sentinel node and no others. BIG mistake as on biopsy the node did have cancer with no clear margins so it was back into surgery and they took all of my nodes some 18 to 19 worth. No other cancer was detected in them. I can't help thinking if the surgeon had taken say 5 or 6 at the initial surgery I might not have required a second op.