Keyboard shortcuts for odd characters

I work with Middle English a lot and would like to have quick keystroke shortcuts for the characters thorn and yogh. How do I set up the shortcuts and, for that matter, how I do I set up keyboard shortcuts for other functions?

I like typeit4me a lot. You set up abbreviation sets for anything you like (symbols, words, paragraphs, scripts, etc. I have one set that spits out html codes (for logic symbols and the like, e.g. ∀) and another for text (same symbols, same abbreviation, different “code”). Nice program.

OK–the trick, at least for thorn and eth and slavic accents, etc–is to switch from the standard US keyboard to the extended unicode US keyboard. This extremely helpful page from Penn State shows how to do it: … acext.html

Still looking for the yogh keystroke, though. Anybody?