(Not a coach just a fellow lifter so take it or leave it)
It looks like you’re getting on your toes on some of the reps. When I get on my toes I try to to point my chest down more and it seems to help me more than thinking butt back. Or think mid foot the whole time. What ever cue works for you. As for adding more weight or working on form with less weight? personally I like adding weight to the bar so I’d do that, plus it is hard to get stronger at weights that don’t challenge you, make sure to take appropriate weight jumps if you have back problems going on.