Fontdatabase.app's aim is to make it way easier to choose and find them. Simply choose the font you have in mind as a base for the search, and the attribute you're looking for, and you're set! You'll find a curated selection of fonts with links to get them. Please keep in mind that attributes such as "more formal than x" or "more informal than y" are bound to be a bit subjective. However, the suggestions were of course curated with design theory in mind, so nothing should be wildly off.