As a service to my fellow bookbinders, I am offering some of the papers I use for my books for you to use in yours! I buy it here: https://www.thepapermillstore.com/superfine-softwhite-paper-25-x-38-in-70-lb-text-eggshell-1000-per-carton.html and get it custom cut.
This is Mohawk Superfine 70# text-weight paper, in soft white with an eggshell finish. It is awesome. It is also grain-short, meaning if you take one of these sheets and fold it in half to make a signature 6.25″x8″, the grain will go with the fold. This paper takes fountain pen nicely and just feels lovely to the touch. I use this paper in almost all of my blank books.
Drop me a line if you are interested in less than a full ream – I can probably fit smaller amounts into a padded shipping envelope if you don’t mind it getting folded in the middle first.