Could you just sew a layer of spacer mesh over some webbing to give you the qualities you need ?
I got curious so pulled my late dad's canvas / aluminum pack out to see what materials were used, leather for the waist belt and some light 50mm cotton webbing for the bands across the frame. Looks just like:
https://lincraft.com.au/products/cot-we ... 3100054659 I'm not sure if it's the best choice, but it's cheap and available at least, should breathe a bit better than synthetic webbing too, just not as sturdy. I wonder if this pack predates synthetics entirely ?