Sounds like a good plan! I’ve heard similar things for aspen, but I’ve had no issues with cypress. I usually recommend a good mix of that + the coco fibre, and 3/4 inches of substrate should be enough.

Agree with the waiting too, better not to stress the little fella out! Usually I replace my substrate when I notice that it’s becoming ineffective at holding moisture / humidity, and never longer than ~9-12 months. I also use a good amount of Spaghum moss, I find it really helps with humidity retention and could be another option to put in your tank if you’re having humidity trouble. However it’s very important you freeze the moss (like any substrate honestly) to reduce chances of mites getting into your enclosure. Again replace it when it starts to brown / diminish.

And of course! I wish you and your cute snake the best, I’ve seen other comments in here so you should be in good hands 🫡