Any diaper is going to leak if it's completely saturated. There's no way around that-- the wet has to go somewhere. So you need more absorbency, or late-night changes. I'm no big fan of many nighttime changes-- with three young children, my sleep is too important not to take every second I can get.
Our solution has always been to increase absorbency to an absurd level. If you're using fitted diapers or prefolds, you need more diaper. Fold prefolds inside the fitteds, or use three prefolds at once. If you're using pockets you need more inserts. If the diaper can't hold more inserts, then you need a diaper with more room. Then you need a full-cut cover, one that's long in the legs and high in the waist.
Hemp and microfiber hold a lot for their weight and thickness, but they also can harbor stinkies more than cotton. So it's a trade-off. I go for the cotton, and live with the bulk.
Our solution has either been an ordinary fitted diaper with two prefolds folded inside, under long-legged wool, or Very Baby Simply Nights fitteds, which come with enormous snap-in inserts. We add an infant prefold or two inside those, and put them under wool.
Baby will have an ENORMOUS behind.
I also second thoroughly lanolizing your wool. Wool washes containing lanolin are fine for maintaining a cover, but sometimes the cover needs something more-- Lansinoh dissolved in hot water and added to a cool hand wash, and a long, long soak with the cover inside out.
I would also really recommend that if your wool isn't long in the legs and high in the waist, that you consider a cover that is. We use Disana covers and love them.
