Did you try the double BOA models? If one of these fit your foot better (enough space for your high arch), why not give them a try? It sounds, as if its not the size but rather the model that doesnt fit.
I have small ankles, high arch and wide knuckles. Had two models of Burton and had big problems with aching/numb feet. They always seemd to put pressure on the arch, even if I bound them quite loose. Tried heat molding and even orthopedic soles but nothing helped.
Since this year, I have a BOA boot for the first time (K2 Contour, double BOA, one for the inner and one for the entire outer boot). My high arch fits into these boots very well, no pressure points of tongue/laces and I love their BOA system. You can adjust the outer AND inner boot on the fly mm by mm while riding till you get the perfect fit. First time in 10 years I can ride an entire day without constantly numb feet.