I have used plastic filing folders (accordion type) and also plastic cutting boards to make reusable liners. If you could find something similar it could work. In this blogpost I included video links that might give you a feel for the material (they are in the stiffer side):
https://soapsbyglenda.wordpress.com/2018/08/20/an-alternative-to-freezer-paper/
https://soapsbyglenda.wordpress.com/2018/08/20/an-alternative-to-freezer-paper/