You might want to try doing a superset of a lower back/hammy exercise and a quad dominant exercise after squats. I find that makes my squats seem easier the next session. For lower back/hams choose good mornings, SLDL, hyper-extensions, leg curls, etc. For quad dominant choose leg press, hack squats, leg extensions, etc. Or if you are really a masochist try power cleans or power snatches after squats!
You also might want to do legs 3 times a week, with a different main exercise each session: squats first one session, deadlift first next session, front squats/power cleans/leg presses in the 3rd session. Or do squats each session, but different rep and set schemes each session: session 1 3 sets of 12-20, session 2 3 sets of 8, session 3 5 sets of 5