Platform behavior objects can use "has a wall (to left or right)" condition. You can use that combined with a key press condition. Check if it works with gravity or with no gravity.
Note that platform objects will still fall down even if gravity = 0 if not on top of solid or jump thru. Set Vector Y = 0 to stop moving vertically (though you want to go up or down when beside a wall, so you probably don't need this)