I have seen a lot of approaches over the years! There's heaps of ideas out there. The old school terry training pants are still dearly loved by many. I have also seen a family recently have some success using empty pocket shells as training pants - the gorgeous child TTd in a few days, as the shells were really easy for her to rip off by herself, but they also held in any little accidents.
I know lots of people who go straight to good old undies, and I think it works best after a few days just at home with nothing on.

So it depends what you want to go with. You want him to feel the wetness, so defs go with something a little absorbent, not anything wicking. You also want easy on/off - so velcro or elastic waist. And waterproof is up to you. I'd be inclined to go with a single thick layer of cotton terry with a PUL outer, in either elastic or velcro opening, depending on what you think he'll do best with.

Does that make sense? Or is it ramble? Sorry...