Never can resist striped clothes! It is on sale in store (item # 2334260000, after an extra 30% off, $22.39), see here.
I bought size p0 from Banana Republic store 8293 (Chestnut Hill, 617-796-9815). P0 is about same as regular xs.
With a skirt (Top: BR, Belt: JCrew, Skirt: Zara)