Any degree of aileron to rudder mix that you choose will only be perfect at one airspeed. At lower speeds, (landing) it won't be enough and at the planes highest speed, it will be too much. When flying inverted, the mix will be opposite of what the plane needs. I suggest just learning to use the rudder.

If you are an inveterate right stick only except to turn the engine off for landing kind of flyer and insist that a Cub accomodates your flying style, you might start out with 50% aileron to rudder mix and fine tune it from there. Cubs actually turn pretty well with rudder only.