i'm a 12-12.5 US in shoes but in boots (work boots, waders, snowboarding boots) i'm a 13. i know boots stretch but i'd rather have some that were a little big than too small. remember you'll be wearing thicker socks.
as far as a wide board, yes, get a wide board. if it were up to me, my skunk-ape would be wider. i don't like looking down and seeing the tips of my boots sticking over the edge of my board but i guess that's just me.