I have tweaked some of the fonts on the site again (but not all of them, so there is a bit of a crazy quilt effect going on here).
Specifically:
Body font: JetBrains Mono
Heading 2 font (used for post titles): Ubuntu Mono
As an added bonus for me, because WP doesn’t “see” JetBrains Mono in the editor, it is using Bold Segoe UI at 17px instead.
I’m all about the monospaced fonts. For now. For today. We’ll see what happens tomorrow.
EDIT: I have already changed the Header font to Barlow Semi Condensed, mere minutes later.
EDIT 2: I've now changed the sidebar to JetBrains Mono and also made the background colour of the site blue, and the sidebar a greenish-yellow. Or a yellowish-green.
EDIT 3: I've updated the blue in the logo to make it a bit lighter and it seems WP just needed to cache the fonts, as the editor now shows JetBrains Mono, as nature intended. More tweaking undoubtedly to come.