You could try Long Tall Sally but their skirts are really overpriced for what they are and I find their sizing is often really weird. I'm 6'1" and I buy most of my skirts in vintage shops (same with playsuits and tbh most of my other clothes). Anthropologie have some nice skirts too, but they are quite pricey unless you can snag a bargain in the sales - I got a really nice mini-skirt in there a few years ago though, and still wear it now - the quality is pretty good. It's trousers I have trouble with - Topshop's are THE WORST for fit!