Hi, I'm in Oz (Sydney) and found 10 1/2 in black knee high boots (small heel) with Sandler about a year ago - my size would be 42/43. Also found some brown flattie boots a little while later in 10 or 11 which fit well (Schubar?)
In my experience 11 is often a good fit, although some boots have a narrow calf and can be difficult to zip up. A lot of shops may not have 11s in stock, but can order in.
Good luck with your search - a good pair of black boots is a good thing!
