You know that 主義 is "-ism." If you add that to being comfortable like you're in heaven then you have lots of optimism. You're sure you'll be okay in any situation!
This is a noun in Japanese but, depending on the context, it's often translated into English as an adjective.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
My older brother doesn't have a social life, but he doesn't mind much because of his optimism.
I don't think anyone is more optimistic than he is.
Fugu is as optimistic as people say he is.