Have you tried a tots bots easyfit? I love them because they have a pocket to add extra boosting. I always boost mine with a little lambs bamboo booster and a easy peasy hemp booster. I've also use a bigger weeds hemp prefold. Lily isn't a mega-wetter but she can easily last a morning at preschool (at least 4 hours) in one. And there is still room to add more boosting if necessary.
I am just trying out new Bambooty Easy Nights which are a night nappy but I think they're slim enough for use as a heavy-wetter's day nappy. Certainly much slimmer than any other night nappy I've seen, and DH didn't even notice they were bigger than the normal Bambooties.