ME AIO. They offer both size large (up to 35 lbs) and extra large (35-45lbs). My almost 30lb. dd can wear both. If your guy is tall and weighs around 30 lbs, I'd get the xlg, although they both have a good rise.
They are a bit bulky, especially if you size up, but they provide great coverage and plenty of room to lay in doublers if you want to. Very absorbent on their own too, much better than the large simplex IME, even when stuffed.
, married to dh for 22 years!
Homeschooling mom to ds17
our 3 1/2 year old potty princess