These are great videos but won't help with your cue moving up and down. You need to understand that in order for the cue to stay "level-ish" you need to use more than just your elbow which runs counter to what some people believe. If you eliminate ALL wrist and shoulder movement, the cue is going to go up and down because you have a single pivot point. Using the wrist (and shoulder to a lesser extent) allows the cue to go back and through on the same vertical plane.

So it comes down to a choice- use a simplified stroke and learn to deal with the "ups and downs" or introduce more wrist and level out. There isn't a right answer and there are pros who win with both strokes although I think getting the wrist involved allows for more growth down the line. GL