The Field Notes Signature size notebook is perfect. This Template set makes an awesome cover that holds the book, 2 different ID/Bank Card Slots and a space for business cards too. You can watch a video of the book being built here:
These templates are made from long lasting acrylic. They make cutting out your leather fast and accurate. Just place the template on your leather and cut around it with a scalpel or other knife. With proper use, these templates should last you forever.