You should stick to the 3hr EASY, until 4 months then switch.
Start with the slow flow teat, if he gets bored of that switch to a medium flow teat.
With my DD I switched onto the fast flow teat at 4 months (recommend age 6 months), but she got bored with the previous flow teats and would not take the bottle due to her sucking and not getting enough milk.
HTH