Hey @gjpierce thanks for reaching out!
Finding the correct boot for your feet is a very important part of the equation for having a successful adventure. Congrats on getting started on the right foot (pun intended :))! For the best boot fit possible we recommend scheduling an appointment with a boot fitting expert through our Outfitting Scheduler at your local REI. They will be able to measure your foot and match it to the best boot for you! 12 D is not technically a wide in footwear, but depending on other factors it may be worth exploring that idea. It will depend on your foot and the construction of the boot.
I hope this helps, best of luck on your upcoming trip!