This is a great beginner book:
https://smile.amazon.com/Handwriting-Analysis-Putting-Work-You/dp/0809235668
I also have trained with an FBI consultant on graphology, body language, personality profiling, and group dynamics. I also have a Master's Degree in Leadership where I use these skills extensively. Parts of my Masters' Degree was an analysis of profiling methods including: Meyers Briggs, Disc, Enneagram, MMPI2, Big Five, and more.
I loved your content as it expressed both interest and skepticism in this. Keep that in mind as this is not an exact science, but tends to work pretty well, especially if someone is not writing with the intent of being analyzed. It is possible to try to game this, but most people cannot fake more than half a page before their real writing gives them away. I won't analyze anyone writing on lined or graph paper or if they have written less than half a page.
Have you looked at digital artist gloves? They cover only the last finger and are used on tablets to reduce friction with the glass surface. It might help if you write a lot.
https://smile.amazon.com/Articka-Drawing-Two-Finger-Reduces-Friction/dp/B09Q963W5P