Fleece is a great breathable alternative to wool. WN & stacinator fleece wraps are a very similar shape to ME airflow. I think fleece wraps keeps them cooler than using pul.
We use WNNN, soy UDNN & HL bedbugs but I don't know if he would get too hot in those. The soy UDNN are possibly the slimmest of those.
Flutterby fluff night nappies are supposed to be slim but I haven't managed to get hold of one of those yet. I will be madly stalking for a couple when the next custom slots go up.