Resources for SPD

Post describing a healthy/adaptive schizoid personality style:
https://www.7cups.com/forum/PersonalityDisordersSupport_81/ResourcesInformationonPersonalityDisorders_459/Personalitystylesthehealthyversionofeachpersonalitydisorder_269564/#forum-post-2868456

A paper presenting a very empathetic perspective on schizoid tendencies:
https://www.researchgate.net/publication/7142775_Some_Thoughts_about_Schizoid_Dynamics

I'd personally recommend anything you can find by Harry Guntrip on schizoid dynamics. I've felt like he has a perspective that is very deep/insightful while still being empathetic/validating and not too technical (compared to a lot of other psychoanalytic authors).
Harry Guntrip - The Schizoid Personality and the External World (1952) [Chapter 1 from Schizoid Phenomena, Object Relations, and the Self]
Harry Guntrip - The Schizoid Problem, Regression, and the Struggle to Preserve an Ego (1961) [Chapter 2 from Schizoid Phenomena, Object Relations, and the Self]

A doctoral dissertation presenting a psychodynamic treatment handbook for SPD:
https://digitalcommons.pepperdine.edu/cgi/viewcontent.cgi?article=1412&context=etd