What was the process for determining that you needed a custom last. Did they get that from your tracing and measurements? I sent tracings to bakers and they said I should be a 10D, and they shipped me an in stock pair of 10D that were not the right fit, too big. I have been toying with the idea of flying to whites to get fitted in person. I also have a narrow heel and regular width ball, but combined with a low instep and half size different feet.
If you can get to Whites, I strongly recommend it. I wasted two boots in two wrong sizes even though I followed the instructions and sent them to Whites. They always err on the side of caution, figuring out that a thicker sock will solve the problem of a big boot, but a tight boot is dead end. Frankly, nothing more frustrating and a waste of money with a wrong size boot. Get it right first time. You`ll have a fun and memorable trip to Whites, and I`m sure they are great folks. Tracing is hot and miss.