Ask about 45 degree leg press or weighted step-ups like Steve Francis uses.
I had pretty bad back spasms (muscle damage, not sciatica) some years ago and my back muscles have never completely recovered, so I personally go with the 45 degree leg press 90-95% of the time. I only go to back squats (not less than 5 reps and never below parallel) for testing. I don’t seem to miss the squats. There’s a conversion factor from the leg press to squats of dividing by 1.8.