For those who found almost the right font but not quite, FontForge is a free and open source editor that's pretty easy to use and even has a tutorial on editing and design:
You mentioned it as being a critical feature but from what I've been reading, it's pretty complex and tricky due to it's weird syncing rules and relationship with OneDrive. The only decent solution requires a Windows version. See: https://answers.microsoft.com/en-us/msoffice/forum/all/good-...
https://fontforge.github.io/en-US/ http://designwithfontforge.com/en-US/index.html
Editing glyphs is just like using any image editor. You can mod any existing font or even combine glyphs from multiple fonts together into one.