If you’re looking for a reasonable FOSS swipe keyboard, try AnySoftKeyboard. While still a step below the non FOSS keyboards I’ve used before like Swiftkey, it gets the job done reasonably well

What about an Android tablet running a custom ROM without GApps flashed, and an adapter for HDMI? There’s a handful of widely sold tablets that also have a decent development scene and are cheap second hand. Check XDA forums for various models before deciding which one to get