What are you just itching to get at?
I have no advice from first person, as I haven’t ever had to wear a cast.
Have had a lot of experience of Ailsa in cast over the last couple of years, and bits of wood seem to be the best (chopstick an excellent choice, also knitting needle as Sandi mentioned).
One thing you may not have thought of, put some cardboard on the sheets.
Ailsa managed to wear through a $600 set of Egyptian cotton sheets with her casts. By the time I noticed the wear it was too late. Those sheets were definitely a luxury item, and we have not replaced them with anything like as good a quality.
So maybe others can learn from our loss.
Wishing all the best for rapid healing, and minimal itching.