It kind of depends on how long your legs are, specifically, your femur. If you are more leg than torso, then I would do a 17 or a 16.5 inch jump saddle. If you havce short legs and a long torso, you migh be able to use a 16.
Will you grow taller? I am not sure you mentioned your age. If you might grow taller, i'd err on the size of slightly larger.
For now, as an above member said, a 16.5 inch, would be my choice.