I found my cowboy boots! After searching without success for ankle-high flat-heeled cowboy boots, I came across these Blowfish Tulsa boots on asos.com. I remembered my friend Liz buying a pair of Blowfish boots so after consultation I took the plunge (they were on sale for $60 so I couldn't resist). I am a size 8 and ordered UK size 7 (which, as it turns out, I need to wear thick socks with, so I could probably go down to 6).
These boots are SO COMFY. I have actually been wearing them around the house on cold days, and I rarely wear shoes indoors. The soles feel like they have gel insoles. And they're still $60 with no shipping!
Now all I need is a shapeless, floral-printed dress and a long brown wig and I can unleash my Prairie Lunatic look on the streets!