During my design of a simple robotic arm, where I 3D printed most of the parts, then used these HS-422 servos, it turned out that for a better control precision and to be able to apply Inverse Kinematic Modeling on my arm, I need feedback positions from these servo, which HS-422 do not provide.

I want to keep using these Servos because the parts are designed to fit them, what options do I have to include feedback position sensors without changing the servos and re-designing the arm's parts? Or is there any servo with feedback position and close dimensions to HS-422 that I can replace with?