I started adding light squat days somewhere around 255-275 lbs. I'd do my deadlifts on light squat days and it really helped to have the reduction in fatigue. I just keep them around 70% of my heavy days and it seems to work well. It's heavy enough I have to focus and do them right, but not so heavy that I am still winded by the time I'm warming up the next lift.
My weightlifting shoes have a 3/4" heel, but I don't know if that's the true thickness or just the heel-to-toe drop. The deadlifting shoes are by Sabo. They're 5 mm in the sole, true thickness. I got the "Pro" ones because I hate cramped toe boxes but I would have been perfectly happy with the normal ones otherwise. I'm sure I'll comment on them once I try them out.