itch.io

from what i can tell you want to keep this a subscription game FOREVER which seems like a really bad idea because you will inevitably stop supporting it at some point (either fatigue, age, or death etc) and then its status becomes unknown because if you dont make it free or publicly available when you for instance die then it would become lost media upon its server shutting down.

personally i think a much better long term plan especially if you intend to keep releasing content is to have the free or one time payment version be several updates or chapters behind or even just making the main story available when its complete and having the "dlc" be subscription based there are a lot of ways to monetize something like this that doesn't require the entire game to be locked away or completely destroyed upon its EOS.
especially considering your current system makes an already niche audience even smaller as a lot of people aren't willing to pay a subscription for limited access like this and EQUALLY im sure there are a lot of people who would subscribe even if it WASNT required