I agree that it is possible to really hurt your foot in bindings too big. the chances are small, but possible!
IDEA #1
However, I will suggest
(but with this suggestion i am in no way saying that company, slingshot, or any other person recommends it and that they or myself are not liable with this idea) That you put a footbed inside the boot underneath the inner layer, assuming the inner liner comes out just like slingshots... even if they DON'T come out you can still use this idea. If necessary you can put some kind of material (i.e. foam from a fun-noodle or something) in the toe box area to "shrink the size down."
I personally used this method to make my size 11 SS D2 boots a size 10.5 (my foot size) I cut up my old 199? Ultra Suctions and put the modified footbeds (bellow pics) under the SS liner inside the shell
Id suggest the size 10 for you, but IF you really plan to use the boots a while and/or you expect your feet to be growing quickly then you could potentially use the same method even for the larger size 11
Company used the same base as slingshot so I'd imagine that the boots sizes run/and feel the same.
IDEA#2
As stated above, wear socks. you could even consider those diver socks that are like thick neoprene socks
IDEA#3
use a combination of idea 1 and 2 ;)
good luck