M.F.
I've never been any good at this. Mainly because sizes in different brands don't match up well. Target stuff is cut a little narrower and shorter, Baby Gap is long and narrow, Gymboree is big all over. Old Navy seems to be the truest fit we've come across for mine. So, I gave up and just buy clothes when we need them. :-)
Note that 24-month typically has "diaper room" in the bottom area. 2T will be a little narrower, and longer.