I wouldn't give a dummy. Sucking his fingers does not require your attention. If he relies on a dummy instead, guess what happens in the middle of the night when he wakes up without his dummy? My DS uses a dummy and when I was unable to wean him off using it to sleep I had to resort to teaching him how to put the dummy in himself so that I wasn't always having to give it back to him. That worked well but I think why make your life more difficult?