> He used to type 90 words a minute, which seems to me quite fast enough

The version I heard was that his dictation favoured conversation which quickly degenerated into shouting quarrels, rather like improvisation by people who aren't very good at it, but would be able to write scripts if left alone for a week.

> without using my hands; how would I write?

Dictate to webcam in sign language. Then your typist can be remote, so it's an ideal solution unless, by any chance, you're not fluent in signing.