My take on EF is that sizing isn't as critical as it is in other brands because so many EF designs are constructed to drape on the body. I've found, when trying on her designs in a dressing room, I can often fit into a S, M, and L--and could theoretically wear any of those sizes depending on what kind of look I was going for with that outfit.
If you are looking for a loose, drapey fit, I'd try the M for starters. In my experience, one of the reasons so many people prefer to size down one or two sizes in EF is because it takes a bit of adjustment to move from tailored or body-con fits to the EF fit where garments getting their shape from the way fabric drapes and folds around a living, in-motion body.