I'm in Oz, not the US, and the boot fit expertise here is for high-performance alpine. The problem is that the fit required for this isn't really compatible with backcountry skiing - especially if one's toenails are to stay attached.
My feet are ~average width at the ball, but I have high insteps and a narrow heel/achilles area, plus narrow ankles and thin shins; overall volume is fairly low. Also, the left foot is one Euro size longer than the right (about 5-6mm). It's very difficult for me to get a snug fit without ending up with a too-short left boot, and heel lift is still a problem with both feet.
Complicating matters is that the places here who sell other than alpine boots don't do any boot fitting and vice versa. With thermo liners this makes it very difficult to guess what size might be appropriate, as it's hard to know how much the various different liners might expand. Flexible soles (and bellows) mean there is a lot more movement inside the boot than with alpine, especially when skinning or hiking.
So, how do I go about making sure my next pair of boots actually fit, and what do I need to tell the local boot fitters to do differently than with alpine???
And, can you recommend any custom/moldable footbeds which are able to flex at the ball of the foot without cracking?