DS is 7mo and has his first two teeth - we used the fingertip papery things to start with but they are v expensive (and some of them seemed to have dried out in the box!) and so we've moved onto an aquafresh first baby toothbrush and aquafresh milk teeth toothpaste.
DS doesn't mind me using the brush - he usually grabs it and sucks on it enthusiastically. More sucking and swallowing than brushing of the teeth goes on...
We only use a tiny smear of the paste and sometimes I manage to get a tiny brush on the actual teeth
Sounds good. At that age he simply needs to get used to the idea of brushing. Allow him to play with the brush himself first and then try to have a quick brush yourself. As he gets used to it, he will allow you to brush more thoroughly. As you said, the toothpaste should only be a tiny smear. That will give him about the right dosage of flouride, which he needs, but should not be given too much.