Back when I worked with commercial patterns I would just sit down in Jo-Ann's and flip through the books.
Maybe some kind of track suit ? You'd have to add the "skirt" part, most likely. There might be a similar coat pattern, or even a mini-dress that you could shorten or something (since you'd be wearing pants under it).
You'll probably never find a "perfect" pattern that needs no alteration, so you have to find some that are "close enough" and pick your battles.
Disclaimer : This post written by a Grumpy Old Man
Actually in the pipes:
- Remaking Ser Loras doublet.
- Luke Skywalker, A New Hope
- Wind Waker starter costume in swim material
Eventually: Paul from Dune, Faramir, Harry Sullivan