Adding this to ye olde FAQ, as I get asked this question a lot.
What specific references were you looking at while designing Jasmine’s costume?
Racinet’s plates were a primary source of inspiration, along with paging through sites about Persian miniature painting and middle eastern clothing terminology. Searching for this sort of information becomes a lot easier when you have some vague idea of what you’re looking for.
Problematic though that final Jasmine piece may be, this is at least a great starting point for period Persian fashion.