Medium flow teat

So my LO is just under a month, we've had to switch him to the anti reflux aptamil and he's been having 2oz of that and 2oz of expressed breast milk at every feed, but he's taking about half an hour to get it out and is tugging at the teat when he's feeding and sometimes get a little frustrated because he can't get it put fast enough, should I switch to a medium flow teat or keep him on the slow flow? I still latch him a few times a day just on the boob and he's still latching really well so don't want to switch and risk ruining his latch, and also aware the age range for medium flow is 3+ months