Id second the LLS ultra wetter though I imagine you would need a custom size. My LO is a year old and 22lb ish and needs large in the ultra wetters (they seem to fit quite a bit smaller than the usual size) You may also be interested in Bedbug Plus in Junior size that Bonnie has just sent out to testers (Im testing one on my older night wetter) they should be available to buy before long and would certainly fit his age and offer a lot of absorbency.
It does sound like the wee might be escaping somewhere if everything is very wet even through wool. Wool is normally brilliant at keeping very soggy nappies from wicking through and normally only 'leaks' if the pee completely escapes the nappy and runs out the leg or similar. Perhaps a serged nappy rather than a T&T may help this?