Go to a good shop with a bootfitter who actually knows his shit. Booster straps will help but they aren't a cure-all. You might wanna ask about these weird foam pads they put in the side of the boot to fill in extra space around your calves/shins, that helped me a lot. Remember though, no matter how good a fit you have you will get shinbang if you land backseat a lot.
I spent three hours selecting the perfect boot for my foot with a guy who's done fitting for like six or seven pros (Matt Manser at Ski Rack for those in VT). I got custom A-Line footbeds, a booster strap, and those foam pads. I've had it heat molded twice. I spent over $700 of my hard-earned cash making them perfect, and they fit my foot better than a tight vagina. BUT, if I land back seat real hard, I still get shinbang. Keep that in mind..