We introduced a dummy in the last week (DD 3 weeks old). Hadn't needed it prior to now but she really wanted to suck (it is a reflex afterall). She is now (excluding today!) very settled and we have had no problem what so ever with the breast feeding. We only give her the dummy when nothing else is working so she isn't sucking it all the time. You could give it a go and if you feel that the breast feeding is effected after a couple of times then stop. The battle is finding a dummy that they will take! Old cheapo tommee tippee was the only one she seemed to like.