i have a pair really similar to that, it's leather with patent leather trim and i make the mistake of getting a 38. I have a slender foot and usually wear a 7.5 but these can get uncomfortable. I think they have stretched a bit from wear and fit pretty well now but I would definitely size up at least 1/2 a size to even a whole size.
I don't own any of their satin pairs, just leather, so I don't know how much give they have... is there a Barneys or Saks near you so you can try them on first??
French brands are 1 size smaller than your typical European size. If you wear an Italian 38 you have to have a French 39. Don't risk it, because those shoes cost a lot of money, you don't want them uncomfortable!