Save typeface when composing messages in Mac mail (Catalina through Sonoma)

Howdy fellow Mac users and gurus,

Is there a way to set the composing typeface permanently in Mail on macOS?

We can set the font and size, but typeface never seems to retain the preferred setting. (eg Helvetica 18 = OK. Light =/= OK. A favorite can be set, but must be selected on every message. Multiple computers, macOS versions, and user accounts have been tried.

I am not opposed to using Terminal, templates, etc to make this change permanent if there is no way to do this via the preference pane.

Thanks!