I ordered my regular size and they fit perfectly.  This is my first pair of Uggs and I absolutely love them.  There is no arch support but that can be corrected with an insert.  I highly recommend these boots.  I am using them as slippers/run errands shoes and they work great!  They keep my feet warm but not sweaty.  Give them a try.  I wear a 10/10.5 in shoes and the 10 fit me.