I wish my gym had a decent back hyper machine. Our one has the axel point positioned right on your balls so every time you extend your back it shoves your balls into it. Get a video of your squat form, at 155lb you shouldn't need assistance work to progress. You can do glute ham raises on a lat pull down machine, but I don't know if you'll be able to do one. My mate who squats 3 plates at about 150lb tried one last week and tore his hamstring on the eccentric. Wouldn't hurt to do good mornings, I love doing them, excited to do some today after ME squats.