Add single bookmark button to top level macOS Safari toolbar

I would like to add a [bookmarklet](https://en.wikipedia.org/wiki/Bookmarklet) to my Safari window on macOS. I want the bookmarklet to be available as a button in the [top-level](https://lapcatsoftware.com/articles/blues.html) Safari toolbar, in the same toolbar as the Back/Forward buttons, address bar, Safari extension buttons, etc. View > Customize Toolbar... does not seem to show any bookmark-related toolbar buttons for this toolbar I'm aware that I can View > Show Favorites Bar to display a full "Favorites" bookmark toolbar underneath the address bar. I can display and click a bookmarklet from this toolbar, and uncheck Show Title to [display only the favicon](https://apple.stackexchange.com/questions/143916/safari-display-favicons-in-favorites-bar) . But I don't want to always see all of my other bookmarks in this bar, or waste the vertical space. I just want a single button next to the Address bar that opens a single bookmark / invokes a bookmarklet. How can I do this in Safari for macOS? If it cannot be done stock, are there any Safari Extensions that enable the functionality?