I have been using formula on the odd occasion since DS was three weeks old. Now, when I say odd, I mean ODD. Some weeks once or twice, sometimes not for two or three weeks. My breasts just don't respond well to pumping, I have to work for a half hour to get two ounces, and I get nothing if I try after DS has just been fed (I know it's not a supply thing, as he is HUGE)
I would hold off until your sin is three to four weeks old, but then try him with a bottle of half formula,half breast milk. That's how I got DS started.
I would love to EBF, but my boobs just don't work that way!
Freya