I have FL fuse zips and I’ll say they’re super comfortable. I didn’t bother with zip offs for kiln. I use the kiln boot tops and have them as my permanent base layer. Albeit, I use them under the corrugate foundry which has hip zips to vent.
IME, you can go with a slightly heavier base...
I used FL corrugate foundry coupled with FL kiln boot top bottoms for CO archery last year. This setup was perfect for me as I get cold easy but able to easily monitor temps with the corrugate hip zips. Temps can feel much cooler than expected with a slight breeze under the canopy at 10k+ even...