May I introduce... the letter Thorn!
You see, the English language has a long and messy history, both in its spoken and written versions. The alphabet we know, love, and wish-we-could-get-that-damn-song-out-of-our-heads used to be somewhat different. W, for instance, used to be printed thus: VV. Because V is latin for U, and hence... double-U. Plus the letter S was printed in two forms: the short S that we still use, and the long S, printed like this: ſ. This of course leads to all sorts of hilarious moments in Terry Pratchett novels whenever words like Press appear as Preſs. It also leads to the modern German letter ß, which is just a compression of ſs.
Most of our current alphabet descends from the Latin script, but Thorn comes from Old English runes, along with the letter Wynn (Ƿ). Thorn is the Th sound that we still use today, either as in 'Thunder' or as in 'The'. It fell out of use back in the fourteenth century, replaced by Th in one case, and occasionally by Y in the other (hence Ye Olde English etc). It's still used in Icelandic, one of a magnificent 30 letters in an alphabet used by about 320,000 native speakers. (Norwegians, meanwhile, have to put up with having only 29 letters. Which is a good excuse to link to this).
But the most important thing here is that I can use it in my book without worrying that it'll come out looking like some kind of machine gobbledigook. Result!