i put mine in a nappy with a pullup on top for a while (at night). they got through so much water/milk at bedtime and overnight that a nappy alone would get so soaked it would fall off them. it was the sticky tape that used to come loose... i suppose some biggish pants over the top wouldve done pretty much the same job as the pullup didnt really seem to do much absorbing really.
god i dont miss nappy days! (i had 3 in them for a while there)
He has 8oz milk before bed but none overnight so not sure it's that he's drinking too much but will deffo try size 5. Just being a paranoid mum I guess...but it's all happened recently and I didn't want to to be health related e.g. diabetes. I know, I know... v paranoid.
tbh DS has 9oz milk still and drinks all day, (he's 2.5) I only really noticed this week he woke twice in the night, but one night he had about 15oz of milk and the nappy was an asda one (don't get them!!!)
alternative is to change his bum when you go into bed if you can do it and keep him asleep?