Swazi uses Polartec, which is the original fleece company that made a polyester wool in the 70s. They were originally called Martin Mills.
Swazi has:
100 gsm microfleece, 200 gsm microfleece, like 280 gsm polar fleece, and 380 gsm polar fleece. I may have numbers slightly off.
Use 100 gsm microfleece if you are just using it for high activity, like backpacking. The 380 gsm polar fleece is ridiculously warm. I would recommend the 200 gsm microfleece or 280 polar fleece for a sweet spot depending on your climate. I think 200 gsm microfleece would be easier to use 4 season, as in cool summers you want some warmth and the 280 polar fleece is more a 3 season. Obviously polyester is flammable so you should wear something over it in fire or a spark will make a keyhole.
It is also worth looking at US surplus polartec grid fleece. It is fleece designed to be more breathable by having airy areas between patches of fleece. Best cheap option there. It looks ugly and if anyone sees you in the leggings, they will do a double take wondering if you are nekkid.
As for wool midlayers, Stanfields is extremely underrated. I washed mine a couple times and bought a size up and it is much warmer now.
Asbell wool is also good if you want a woven wool.
