Dearest muse - I would only ever use a freshly cut birch switch on as pretty a bottom as yours. The switches to which I referred are used ones. I never use a switch twice, but find that the sweat that adheres to the "business" end after a thorough switching adds a piquancy to marshmallow - even the semi-edible 'Kraft' variety.
Willow I abhor as being far to soft to provide the sting that should accompany a good birching. Now, be a good girl and go and cut a dozen suitable birch switches from the grove behind the garage and bring them to me. I'll use the finest on you directly.