I still think that you can’t change to guided because it can’t calculate its position. When using GPS it can know where it is, but without it can’t. Setting origin is just a start, you also need something else to get new position updates(e.g. wheel encoders).
Non-GPS navigation is a challenge and will need some extra work. I agree that beacons might impose a too large restriction. However, I am not convinced that visual odometry is less work than retrofitting wheel encoders. You already have a companion computer, which simplifes an eventual visual odometry setup. If you have the budget you could consider the Intel T265 (e.g. this toutorial or this approach. I have tried neither.).