You're doing great. Keep working with that weight until you can get some more depth. See if you can spend some time at the bottom and sort of "wiggle" a little more rom into it while maintaining your back. Think about "stretching" your body and spine to the sky..that will help you achieve it.
Once you can get more depth and it feels better to you add some weight and then do the same thing as far as only going as low as you can stabilize it, etc...
But at the same time keep practicing with the empty bar and working on range of motion.
Try to tweak a little bit more rom into each weight that you work with.
Those oh squats really look fantastic and your lower back is great.