I found with my ds, I really had to catch him in the right sleep stage to do a df. You may try experimenting with your ds to see what part of the sleep cycle he is best at remaining asleep at.
Mine slept in the living room during this part of his life, so I just kept the lights out and quietly snuck in to feed him about 10 minutes after I heard him "transition" from deep to lighter sleep. He usually fed well and went back to sleep. Our df only lasted until 8 weeks, when he started waking more often during the night for gas. When I stopped it, he slept through, which is pretty rare.
Best of luck!