Help! backstroke!

My backstroke is awful. I have no video to post presently, but I can tell you from seeing myself, I know that I am snaking really badly, wasting energy going from side to side and not having my hips and shoulders rotate as one. I've been mainly doing these drills: kob with hands at sides + rotation, 6k1pull, 6k3pull, 2R2L4alt. Have also tried holding a buoy at my ankles. I watched this video, www.youtube.com/watch, and came to believe I am making every mistake possible with my arms that is shown in the video. I can't feel where my hands are entering relative to my shoulders and I'm pretty sure I don't have enough elbow bend. Does anyone have any favorite drills I can work on to reduce my snaking? In a perfect world, I would like drills where I can feel when I'm doing something right or not. The only feedback I have now is the clock and it doesn't seem to want to budge. :frustrated: