Well, IMO stretching and or flexibility work, can be done perhaps 3x weekly pretty much consistently. If one backs off of it, (from my experiences) the muscles/tendons/ligaments will again adapt to only the ROM they are getting. Especially if much of the work is done with arms only in front of the body, without overhead and or rotator cuff flexibility work.
Short answer on the squats is, no. Why would you "have" to squat? Unless you were PLing in a comp and wanted a back squat number!?
Plus, doing front squats is probably more effective than none at all. Lots of oly lifters thrive on fronts.
As was mentioned by "TheMovement" above, goblet squats can be an option or...
Hip belt squats
Zercher Harness (more like fronts however)
Trap Bar deads or suitcase lifts from deficit
Frank Zane Leg Blaster
https://www.frankzane.com/shop/frank-zanes-leg-blaster/
Leg Pressing
If you are so interested in back squats and still want to...
Have you had someone with experience look at your form?
If your knees hurt from back squats, is your knees tracking over the feet?
Have you tried other shoes, slight heel, no heel?