Well since no one else has chimed in yet: I can't say I've shopped at any of these locations but can give you some insight into the shopping districts. The town that is more of a "where the locals go to shop" is Bakirkoy. Some of the more touristic and therefor more expensive districts are Etiler and Taksim. You might want to start with Edip Saat in Bakirkoy unless anyone else can jump in and let you know something more specific.