Their is bodyweight for the posterior and lower body other than air squat. - Pistol squat, shrimp squat, sissy squat, nordic curl, bridge, sprint and many more.

And the progressive overload can be done by exercice variation, you do an harder one.

Exemple: incline push up -> push up -> diamond push up -> pseudo planche push up -> push up on gymnastic ring -> bulagarian push up on ring -> one hand push up.

The current bodyweight fitness is way way past just increasing rep on easy exercice.

I recommend the Recommended routine on reddit /r/bodyweightfitness to start: https://www.reddit.com/r/bodyweightfitness/wiki/kb/recommend...