Now that you’ve experienced making your own paper, you might be interested in checking out this video of paper making genius (literally–he won a MacArthur “Genius” fellowship for his work) and historian Timothy Barrett attempting to recreate the exact workflow and pace of work of paper mills at their prime.
The video of the English paper mill that he mentions is here: https://www.youtube.com/watch?v=Xs3PfwOItto
You might also be interested in exploring some of the watermark databases currently online. There are several, each with strengths in various time periods or regions. One of them, the Gravell Watermark Archive, has gathered links to several of them in one place.