I had him on pur slow flow teats and they are way too slow for him.
The teats i am using now were on a pack of bottles i bought from big W, they are a little fast so he feeds are pretty messy but he seems to be keeping them down.
I would try another medium flow teat brand as they all vary so much, i know it works out a bit of a waste of money but when feeds are taking forever in the middle of the night i think its worth it