What's another word to mean "a way of thought"?

Perhaps you are looking for:

Frame of mind: mental attitude or outlook

I think you are looking for words like 'opinion', 'perspective', 'conception', 'assumption', 'presumption', inference', 'point-of-view' etc.

Weltanschauung is a germanic word with an English usage that correlates to this. It translates literally to "world view" but, as M-W defines, means "a comprehensive conception or apprehension of the world especially from a specific standpoint."

That may be too broad for what you are looking for. You could also try "solipsistic" "characteristic" or "idiosyncratic."

The phrase "state of mind" describes what you're after.