We have done bambino mio training pants. They are terry with some plastic or something in them. They only hold 1 wee and will allow clothes to get wet. But they seem to keep wee off the floor.
DS2 is 20 months too and tells us weewee when he is doing a wee but unless you put him on the potty every 2 hours he won't wee on the potty.
Good luck Dr Tal