I think the lightweight stuff is really what you should be using, it's going to be the most comfortable (it's also a bit cheaper). You should be able to get that form fitting look just by fitting it correctly. The inherent stretch in the lightweight leather will take care of the rest. As I see it (and I could be missing something here), wetforming is really only beneficial when making things like leather cases, where you want it to take weird tight corners.
You can actually sew leather of any weight. You just gotta punch the holes first and then handstitch it. The stitch wheel shows you where to make the holes. In the proper technique, you alternate between the needle and the hole punching awl in one hand. But I cheat and punch all my holes with a Dremel, or drill with a tiny jeweler's drill bit.
To get that butt-joint type stitch, you sew a pattern that ends up looking like 'X's on one side, and like horizontal bars on the other. Actually, there are probably a number of stitches that work, but that one is pretty common. (A leather shop near me has a snazzy specialized machine that can actually sew that stitch automatically. One of the wildest things I've ever seen, oodles of moving parts, and looked like it was at least a hundred years old.)
Oh, one other thing. If dead set on trying to wetform it on the guy, do keep an eye out for signs of hypothermia. Water doesn't have to be very cold for it to happen. The evaporation of the water pulls heat off the skin. I don't think it's very likely, but it isn't something to play around with either.