Welcome to Permies, Joey!
And welcome to the 'let's renovate this ancient farmhouse in central France-club' , I'm here too, and know of some others around us
A bidet attachment to a compost toilet sounds like a good challenge. I think you'd need to have a urine diverter, and probably some means to warm up the water of the bidet in the winter?
I personally don't know of anyone who's combined bidet and compost toilet, but am eager to find out the results to your question.
Here's the motherboard to how Permies works - happy reading, writing and communicating!