I'd stay away from the smith for many reasons, but the main one I'll bring up here is that it won't help you sit back. I agree with Jake that it will probably make your situation worse and get you no where closer to getting your free weight form down. On a smith you can kick your feet out in front of you and push back against the machine on the way up. This does not duplicate a free weight squat, plus will take out a ton of the much needed stablizers to help aid in begtter squat form. If you want to have better form, practice. I realize you say you have tried everything, but you haven't. Go with the box squats that enrage suggested. Do them light til you get it. Learn the proper form on them. Also, starting on a higher box and gradually lowering it will help you to perfect your technique.