I also have a chronic back problem and have had a couple of lower back surgeries (Car accident, long story..). I also thought about cutting out deadlifts altogether from my routine but it's too important of an exercise to cut out completely. I usually start with a very light weight, concentrating on my form (Start with just the bar or light dumbbells). I still can't dead lift a lot but i just concentrate on my form, reps and, intensity. For squats, try doing it on a smith machine first, and then slowly cycle off on to a free bar.