I’m pretty much doing what you’re thinking about, here, and I’m enjoying it, particularly since the developer’s doing quite a bit of work on it at the moment.
Getting your setup to work similarly to the way you have it in OF might take some effort, but it can be done.
Well, mostly, anyway. As always, it kind of depends what features of OF you’re using now and what you can live without.
There are definite limitations (eg sharing) with GoodTask, but it’s a clever hack/superset of Reminders using Apple’s iOS underpinnings.
Federico Viticci over at MacStories has recently switched to it, and built up a number of Siri Shortcuts for it, IIRC. But Viticci switches often from one task management system to another, having rhapsodized most recently about Things, and then 2Do, and then Todoist before that.
It’s a good app, and not expensive, and you get 14 days to play with it unlocked before it goes back into its limited mode. Try it.