> They use Vellum paper that is much better that today's but require killing hundreds of animals each.

Yes, but also, it's more of byproduct. You raise sheep for wool, they're going to lamb every year, you eat most of the lambs, someone buys some of the skins to turn onto vellum.

The processing to produce vellum would be expensive, and not something every shepherd would be making at home, but the input sheepskin would be plentiful.