HI, there is a html game called THE ALTERED VISION.The game includes scenes within your interests such as the chastity cage, scenes with the mother, and others, so my suggestion is to make a story based on the relationship of the MC with the mother, as in the mentioned game, without many characters. I can imagine such a theme with your writing would be a great thing. You may need to try the game to understand what I mean, and I hope that will inspire you in your upcoming stories.