Is there a font that would be easy for me to read with practice (and maybe offer some benefits over Latin characters) but would be illegible to normal people reading over my shoulder?
Google turned up a lot of discussions of writing systems for conlangs, but nothing that’s actually usable.
https://en.wikipedia.org/wiki/Shorthand
https://en.wikipedia.org/wiki/Stenotype
Short of court stenography (which uses pre-existing letters in unique combinations and meanings) I don’t think you can expect to replicate a custom shorthand font on a computer, on account of how a computer processes words and letters.