if you gotto buy online and you have wide feet, salomon is definitely a good place to start.
Salomon have a wider toe box than many other brands, for ultimate toe comfort (which I think is one of the most important features in a snowboard boot). Even their regular width boots are slightly wider than most brands (although I've heard their "wide" models are horribly wide, niche boots). Good heel hold (although part of their tech actually pulls my sock's heels down) and their quality isn't what it used to be, but still on par with most other popular brands.
start with one size down from your regular shoe size and go from there. That's the best you can do in your situation...good luck.