Oh, where do I start and not be proselytizing ... Footwear and proper sizing is a big issue for me. I have a wide foot, tall arch and high instep. "Normal" sized footwear doesn't work for me. In short, it really doesn't work for anyone, most people just don't know it. Although a "D" width is considered most common, modern footwear is not designed to accommodate the natural shape of a human foot. Modern people's feet have been unknowingly distorted since we were little kids by various forms of footwear that were put on us. Of course everyone has different shaped feet with differing proportions. Our feet should be widest at the ends of the toes, not at the outer toe knuckles. No one needs elevated heel, arch support, toe lift, rocker, cushioning, etc. Well, except for people who have worn shoes all of their lives and their feet are weak and therefore need all of those "benefits" that modern shoes offer...
But, we live in a world were shoe design and sizing has been standardized, and unless you want to go with one of the few small companies that makes foot-shaped shoes and boots (and most of those offerings are cheap and ugly), you have to play the game. The biggest problem with shoe sizing advice is it's generally just about the length of the shoe compared to the foot. There are too many other variables to consider for proper fitting.
As mentioned above, the Brannock device is a good place to start (if you haven't) as it measures total length, width as well as length from heel to ball of foot. It doesn't measure arch height and instep volume though. Shoes are sized by length first, but don't get attached to that number. The shoe needs to bend where the ball of your foot is for proper flex. The width at both the heel and forefoot needs to be proper so as to not allow slip or constriction. The volume over the instep needs to be sufficient for adequate lacing without hot-spots. Arch support is nonsense. No one needs it - everyone's feet are perfectly fine to support themselves. They are just weak from being supported their entire lives. If you think you need it, their your shoes.
If you're not familiar with the Munson last, look into it (I didn't know about it until I started hanging out here). It was designed by a military doctor in the early 1900's to fit the most soldiers feet. It's wide at the forefoot to accommodate a natural foot shape and not cause blisters, fatigue, etc. with lots and lots of walking. There are a couple of companies that use the Munson last, and several that reference the Munson last when describing their own in-house last.
After all that, my advice is to find footwear that's offered in wide sizes and don't be concerned about sizing up in length to get adequate width and volume. If you go with a brand like Russell, White's, Wesco, etc. that does semi-custom sizing, they have a wide catalog of sizes to choose from. See if you can get them to do an E width at the heel and a EEEE width at the ball, and extra high instep volume. For example, my foot measures a 9 in length, but to the ball of my foot it's a 10. EE width. To get modern, off the shelf footwear to work for me I usually have to get E or EE width and size up to a 9.5 or 10.
I have a pair of White's SJ that I had rebuilt; they are 8.5 E with standard arch, and they KILL my feet now. I can't even wear them for a few hours. Someday I'd like to have them rebuilt again in a larger size with no arch (but primarily for better construction as the rebuild job they did was pretty bad). Russell Moccasin made me boots (after over a year of back and forth sizing issues), dead flat with no heel, Munson last, 7.5 E at heel and EEE at ball, extra high instep. they're probably the best fitting pair of boots I've ever had. I also have Grant Stone Diesel boots in a 9.5E, but their last runs large and I could have gone with a 9E. They have no arch, and were extremely comfortable out of the box for me. I've been sized for Redwing, and I need a 9.5EE for boots made on their No. 8 last (Beckman, Iron Ranger, etc.). Maybe look at White's Swing last, and Viberg's 2040 or 2045 last.
Sorry for the long winded post. I hope that helps. Cheers! mpp