It seems like we are the same size. Chanel runs a bit small. For my platform pumps, 8.5 fits me, but I ordered a size 9. For all my heels, I always put a pair of soft rubber soles in the front part, so they are more comfortable. In your case, since it's hard to exchange, I would order a 9, it's better to have it a bit loose than a bit small, and you can always put in a pair of soles.