You should work your way back up throughout the season. I'm 5'8" and 135 lbs. I ride on DIN 8 or 8.5, still to be determined for my new skis. But on my park/groomer/messing around skis I have an 8. You should be on 6.5-7 for first day since tearing the ACL, then gradually go up to 7.5 or 8, depending on how hard you ride and how comfy you feel ripping it your knees.
Continue the movement, rhythmic flow
The mind will enhance the down to earth vibe
And then we switch up the style, stance real low
Shattering the status quo, keeping it fly