I'm guessing I found this a bit late Yael, but hope something's helpful.

Pockets and AI2s are basically the same premise just the way the absorbent bit is held in is different. Both are a shell with either a pocket to stuff or snaps to hold the boosters in place. Shells can use either wool or fleece or PUL. Fleece is best at night I'd say for what you need. PUL might cause a bit much sweating. It doesn't breath much.

Press studs aren't as sturdy at snaps. Snaps are metal or plastic and have a couple of parts instead of just the bit you sew into the fabric. They would be far more stable. A hammer in kit would do the same job. The only prob you might find with the hammer in metal ones is rusting due to the long time exposed to wetness.

I have a few patterns I can send you, but an experienced seamstress should be able to draft one off a nappy that fits him (sorta). Pocket is probably easier to sew for an inexperienced nappy maker. It's just the waterproof bit and the microfleece/suede cloth inner sewn and then turned and top stitched together and then all you need to do is sew the boosters.
Trifold boosters work well. They are just two-three layers of bamboo fleece sewn in a large square and then folded in three. You'd need at least 12 layers though I'd say more. People might tell you to use a less bulky absorbent material but in all honestly it just will leak. Microfibre and zorb (man made materials) are prone to compression leaks once they're full to capacity.

Will be back once I've charged my battery. Can send you some links if you're desperate.