I also like Naartjie for the stretchy pants that my tall, thin older DD simply insists upon (she refuses to wear jeans, too, even though she would look SO cute in them!) All of their clothes are soft and stretchy, though I will admit that their sizing can be a little wonky at times. It's not often, and I find that if I stick to their stretchier (i.e. tighter) clothes, like leggings, we've never had a problem. It's things like their wider leg pants that can sometimes run a little big in the waist
They are pretty strictly West coast, in terms of brick and mortar stores, but you can find them online, too.