We use "warmth" but not "coolth" – at least, not usually. New post on a rare word:
https://stancarey.wordpress.com/2024/08/16/birth-of-the-coolth/
Pleasantly surprised that my post on "coolth" has flushed out a couple of readers who regularly use this super-rare word
More on "coolth" at Language Hat: https://languagehat.com/coolth-shorth/
I've updated my post with other marvellous -th words from the OED, including arghth,* blueth, frumth, gloomth, ortrowth, and rimth: https://stancarey.wordpress.com/2024/08/16/birth-of-the-coolth/
* which sadly does not mean what I hoped