Look at Greg's page on dynamic ribbon menus.
Dynamic Ribbon Menu by Greg Maxey
Conceivably, you could have templates for your different documents stored in a folder and have Word give you a dynamic menu of those templates on one button.
Here is such a menu. Everything on it is a template. Change the templates, change the menu.
This is not a one-day project and you will need to learn a lot, but long-term it is worth doing. Again, it is not something done through the user interface. The menus above have worked for my office for more than ten years through five different versions of Word.
Start with Greg's basic page:
Customize the Office Ribbon (It doesn't take rocket science) by Greg Maxey. Be prepared for some frustration.