That's a great idea! A lot of babies find their thumbs between 3 and 4 months old, and are a lot happier for it.
Is he taking good naps during the day? Sometimes if babies have short naps, they're overtired, and wake frequently like you describe through the night. If that isn't it, I'm guessing something is waking him, be it his teeth or his body. And he isn't putting himself back to sleep, which a lot of babies won't/can't at that age. So that is why you're having to help him. I would keep trying to get him to sleep without feeding, except once or maybe twice in the night he may still need to eat at that age.
Another idea is to stop the dreamfeed. If he wakes, get him to sleep without feeding. My ds woke up for his dreamfeed and then woke several times after that, it was like his sleep cycle had been interrupted and he couldn't get back into really deep sleep.