Where do you need the extra room, at the ankle or the instep? I don't know if a size up would give you much more space! Since they are open toe I'd say the length is ok, maybe?
Any time I've bought ankle strap styles I've had to have another hole punched in the strap as my instep is high. Just thinking out loud here!
EDIT I see they fit you perfectly, so I'm not sure what your concern is, as leather usually stretches a bit over time anyway.