This sounds like a scenario in which you could use IKeyValueService. It does save a row in the database, but otherwise it might be the "helper" you're looking for

https://our.umbraco.com/apidocs/v8/csharp/api/Umbraco.Core.Services.IKeyValueService.html

There isn't really any documentation besides the above reference documentation, but you can get an instance like:

IKeyValueService kv = Current.Factory.GetInstance<IKeyValueService>();

// Retrieve the "Hello" key from the database
string value = kv.GetValue("Hello");

// Set a value for the "Hello" key in the database
kv.SetValue("Hello", "Some value");

I don't know your specific use case, but having this in the database would generally be considered safer than having it in a file on disk.