If you struggle to maintain a neutral spine when deadlifting or squatting, or sitting for that matter, a “bit of gaffer tape” either side of your lumbar spine can give some very useful feedback. Set your neutral back, and get someone to stick tape either side of your spine ( the boney bit in the middle): when you stoop it pulls, and reminds you to maintain a better back position ( but don’t tape into a hyper- lordotic position!!)
Obvious point, but make sure you are not allergic to the tape you are going to use! This can really help you save your back and cut down your pack pain. Essentially it tells the body where your back is. Often back pain sufferer’s have no idea what their back is doing.