I have Burton Imperials and they fit true to size. I wear an 11.5 for normal shoes and I wear those for boots as well. When you order them, they may feel tight at first. They SHOULD feel tight when you are first standing up in new boots. If you kneel down into a riding stance, then you will feel your feet slide back a little bit.
After you wear your new boots for a while they will break in, which makes them even more comfy. When I first buy a new pair of boots, I try to wear them at home at night for a little bit to break them in before I go up and use them.
So, if you are buying online, read the reviews to see if people are saying they fit true to size or not. For me, with that pair of boots, it was the same as my regular shoe size, so you should be fine.