Additional Substitutions for Whole Words Only

What it says on the can. My fingers often outstrip the speed that my keyboard can accept input and so occasionally drops letters. Is there a way to set it so that “fr” is corrected to “for” but “from” does not become “forom”? Or “th” becomes “the” but “mouth” isn’t corrected to “mouthe”?

I’d use TextExpander snippets for that. I’m on a Mac, but there are equivalents for Windows.