I think that since /ʃ/ is spelled <x>, /t͡ʃ/ may be spelled <tx>, but I think I will stick with <ch> for now.

My next step has been to work on personal pronouns:

Although Old English had lost its reflexive pronoun, Kastixex redeveloped one from borrowing from a local Iberian Germanic language.

Here is the declension of an example weak masculine noun, zenaba /θeˈna.ba/: