In reply to tnj:
I have a similar problem with narrow heels, although I have fairly wide feet at the front. I discovered that La Sportiva boots work really well for me - started off with Nepal Evos, then decided they were unnecessarily stiff for the level of walking/mountaineering I do these days, and switched to the Trango Alp last year. I find them really comfy for walking in, warm enough for me, (and they could be beefed up with a Yeti gaiter if need be), and stiff enough for the sort of grade I/II winter climbing that I do.
If you're looking for something stiffer, you could go either for the Nepal EVOs, or the Trango Primes if you can get them in the UK?