I have average/lil bit heavy wetters, but here is what I would try. Skip flannel & any suedecloth/microfleece as they just take up space. I would trifold a 3 layer hemp fleece doubler -- make sure it's as big as possible -- 4-5 inches wide when folded & from front all the way to back. Same with the microfiber towels. I'd skip the velour as well for nighttime. I have occasionally used a polyester outer on a dipe to encourage the wet to travel all through the dipe instead of straight through, iykwim. You could try using 2 covers as well. I have had a lot of luck with pajama/diaper cover pants. 2 full layers of fleece made with a BIG bubble butt. Remember, the tighter the cover, the more quickly it will wick through. You could also get some wool, felt it as completely as possible then make a 2 layer cover with it. There are wool doublers out there too (knit or crocheted) -- I cannot remember who makes them, but they go between layers of dipe, or between dipe & cover.
Hope that gives you some ideas -- oh, one more. How does he sleep? On his side? belly? Take that into account too.
PS, I wasn't in love the lightweight windpro I got -- or the heavier stuff either, now that I think about it. I actually prefer the fuzzier joann's (200wt?) stuff. 2 layers work well...I wonder if the more loose pile helps it not compress as much? Hmmmm....
Hope that gives you some ideas -- oh, one more. How does he sleep? On his side? belly? Take that into account too.
PS, I wasn't in love the lightweight windpro I got -- or the heavier stuff either, now that I think about it. I actually prefer the fuzzier joann's (200wt?) stuff. 2 layers work well...I wonder if the more loose pile helps it not compress as much? Hmmmm....