Make the newest version major version paid/available for a sub on Patreon or Subscribestar while the version one update back is free. (most Bugfixes are free too).
The monthly subscription will pay out the most in the long run, funding the continued development, while making it ultimately free awards those who are patient.
Check out a pair of games called Trials in Tainted Space and Corruption of Champions II. That's how they do it and they have been doing well for a long time.