How do you sense your body? How do you sense your body’s alignment? That may depend on how you define your body.
Proper asana is not limited to the alignment of your physical body; it also includes your emotional, mental, and spiritual bodies. Perhaps you experience comfort (physical), calm (emotional), or clarity (mental) during a sitting. Perhaps just a few moments of any or all of these.
Balance in the subtle bodies provides the stable ground for samatha, or the state of peaceful abiding. From here, you have access to the luminescent nature of your being.
Happy meditating.