M3NTALYour best bet is to go to any footwear store and get your shoe size measured with a Brannock device. Bonus points if it is somewhere who can help you do it so you know it is right (not some teenager in an athletic shoe store). Nordstroms for example would be a good place to go.
M3NTALPersonally, I would go with the 10. I've had boots that were a bit tight so I could only wear thin socks with them, and I generally would prefer to do the latter.