I found when my daughter got a bit bigger we were unable to use some fitteds at night. Ive never used the UDNN but had the WNNN and Little Kiwi Quick Flips, with every combination of wool or wrap, and they still chafed the top of her thighs leaving her very sore
The only thing I could do that stopped the chafing, was to use 2 fleece liners, and made sure they came out of the leg opening of the nappy and around the nappy a little so the fabric of the nappy wasnt touching her legs, but made sure it was tucked inside the wrap. I did use Ellas House Bumhuggers and found their ruffled leg openings helped and they were fab nappies too until Evie outgrew them
In the end I resorted to using a standard Nappy by Minki, we never had any problems as there was no wetness touching her skin at all.