Please avoid prescribing best practices without understanding the architecture OP is working with.
First, you don't actually know that using SQLite would make the OP's app stateful—if datasette is set up in immutable mode, then the .db files are no more indicative of a stateful process than a static CSV or a JSON or YAML config.
Second, not every app needs to be a 12 factor app, and you're not in a position to understand the trade-offs OP is dealing with. "Best practices" rarely are best in every circumstance, and often conflict.
First, you don't actually know that using SQLite would make the OP's app stateful—if datasette is set up in immutable mode, then the .db files are no more indicative of a stateful process than a static CSV or a JSON or YAML config.
Second, not every app needs to be a 12 factor app, and you're not in a position to understand the trade-offs OP is dealing with. "Best practices" rarely are best in every circumstance, and often conflict.