The Health Craft Depend-a-Bar Pivoting Grab Bar does not slide up or down. The bar only needs a 1.5 inch clearance. It pivots 180 degrees so it could be moved out of the way to get seated and then pulled closer to help with standing, and pushed back out of the way to exit.
Another possible option is a raised toilet seat or a toilet assist like the Carex UpLift Commode Assist (Product #: CUT200).