Try using your Windfoil Board and same Foil setup you use for Windfoiling. You will be surprised how well that works. The RF 81 should be more than big enough to keep you afloat. Just take off the straps.
For really light wind I use my old KiteRace Boards with Windfoil Foils. This actually works better than SUPs and Surf foils in light wind.
https://www.facebook.com/kitechino/videos/528727078021999/

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Gunnar