Low interoception — would a FitBit help me find a brainspot?

I’m supposed to identify when an eye position reveals stress in any particular part of my body, but so far I can’t. Part of the issue might be that I carry tension in my whole body 24/7 so any increase isn’t noticeable. Therapist hasn’t noticed anything when watching me.
I was thinking maybe a heart rate monitor like a Fitbit or Apple Watch could provide an objective measure of heart rate and tell us which eye positions increase my stress. Anyone have thoughts on this?