No worries Having been there before, it was stressing me out for a while and I was dreading every feed time!

It could be that 240ml a bottle is too much for him? I think at that age DD was only having at the most 180ml, but was probably closer to 120ml and having 6 bottles a day. Maybe you could try more bottles per day with a bit less milk? I agree, if he has had the same teats since day dot then i wouldn't worry about messing around changing teats and bottles.