Whether you use a hand sautillé or a forearm sautillé there will be some vertical movement in the bow stroke.
This clip shows a way to develop the vertical component of the bowing action. You can see that as the screw of the bow dips down the tip of the bow moves up.
Experiment with differing finger combinations on the bow to amplify the vertical or horizontal component. To make the stroke more horizontal, work with just the 1st and 3rd fingers on the bow. To make the stroke more vertical, use just the 2nd and 3rd fingers on the bow.
The contact of the first pad of the 3rd finger with the stick is very important in both combinations.
Note - The first pad of a finger is the soft fleshy part of the finger near the nail.
Acknowledgments to Sheila Nelson. Many points from this routine follow her teaching of sautillé....