I second that a coach would be good; I understand that is hard depending on where you're at; I'll probably do a month or two with SS online once I get the tripod I just ordered.
Absent that, just go lower by going lower; I highly doubt that flexibility is the issue. I don't think a tiny bit of butt wink is the worst thing in the world (video by Juggernaut coach Mobility Myths with Dr. Quinn | Butt Wink | JTSstrength.com - YouTube), it's probably better than high squats with more weight than you can do with good form.