My wife and I are pretty serious bullet journalers. We started off just using marble notebooks, but after a few years we started to make note of their flaws and start making our own versions.
My first attempt was a leather bound journal with graph paper and a pen holder on the side. I laser engraved the Vector Space logo and my name so that no one would confuse it for their store bought journal.
My second attempt got a little more serious, with wood covers, laser engraved front, inside front, and inside back. The pages are custom printed using a LaTeX and Python program that I wrote. LaTeX generates a dot grid, then Python overlays page numbers in the proper order. If you don't think this is a big deal, you haven't thought about the order of page numbers in a book with multiple signets. The signets were bound with a coptic stitch.