Fine, make it Helvetica plus whatever other shapes you need. I would assume that Helvetica includes most of extended unicode, since it's such a widely used font, but I could be wrong, and it's beside the point.

If the computer is the one transforming your writing it should be perfectly quick.

To be clear, afaik current handwriting recognition software is not good enough for this. But if we had software that could transform bad handwriting into good handwriting, why not go all the way?