There is a step missing between harvesting flax and weaving: spinning! I assume the weavers are presently doing the retting, breaking, and spinning of flax, but what if this were done in its own separate building? The spinner would be a tier-1 building that produced thread as an intermediate product. Thread could then be used for weaving, book binding, shoe cobbling, candlemaking, and some types of armor like hauberks. Since the spinner would be a tier-1 building, willow or some sort of marsh reed could serve as a gatherable fiber as an alternative to flax.
I also suggest adding ropes into the game, since ropes were around since ancient times and a lot of buildings and also wagons have ropes in their models. The spinner would also create ropes, and you would need one to upgrade the town center. Ropes could possibly decay over time like heavy tools. To compensate for the addition of a new profession, weavers would be reduced in number and work faster.
Thank you for reading my blog post.