Do whatever works for you. If a dummy is doing more good than harm, then keep using it. Try not to worry too much about what will happen 2/3/4 etc months down the track.
DS had a dummy from 1 month up until about 8 months. He liked it but it got to the point where he saw it as a toy rather than something to soothe himself with - he would just flick it and wave it around. I packed them all up one day and I don't even think he noticed.
I just wanted to add... obviously DS doesn't have a dummy anymore, but he's still not sleeping through. So in my case having or not having a dummy made no difference.