Thanks everyone, I should also have said it's a woven fabric I'm after. As a fat lass who sweats a lot
the fabric needs to be fairly thin and probably not a waterproof as even if it says "breathable" it won't be breathable enough in the, err, important areas.
I've found bi-stretch gabardine at Myfabrics, the sample feels really nice and very stretchy, but it feels like it would soak up water! I might just get some anyway, and wear on dry days!