I bought some loafers and i'm normally a 38, but a 39 fitted just fine
With my mules, the 38 was fine.
I really guess it depends on what style your getting
but if your getting heels, then get a half size bigger, and at least if its loose, you can put those heel grips or sole cushion thingys to make up the difference.
I find that Prada runs about 1/2 size large on me. My feet are wide and I generally wear 38.5 or 39 in Manolo, Choo, Chanel. My Prada shoes are all 38. Maybe you can try going to a B&M store to try some on first?
I have very wide feet, so I always go up in size with every shoe. My feet are actually a 5-5.5 but I always buy a 6.5 in shoes and 7 in boots (so I can wear socks if it's cold). I haven't found that I need to go up in Prada, I wear 6.5 in Prada and 6.5 in all other shoes.