A.H.
I think apparel for everyone is sketchy as one size is not for all in any brand. Especially if you pick two sizes that are the same and they both fit completely different! (And this happens a lot for me, as well as my son.).
My son is the opposite, as he is on the skinny side. So we buy and use the iron-on hemming - it removes rather easily. Or if you hem creatively, you can take it out later. We usually just put a small cuff on him - whether it's "in" or not, I just don't want my son tripping.
If the store/brand you like is picked over, do they have an online site? You may have better luck.