I have written a little step-guide to install a WatchTower image which will monitor the running Docker images (NextCloud / Collabora / OnlyOffice, Spreed.me, etc) and download the latest version if any is available.
I hope it is useful for others to make certain bits more automated.
https://wijman.atlassian.net/wiki/spaces/LIN/pages/491528/Automatic+Docker+Images+Update
UPDATE2: Have been able to restore my server and have re-created the how-to.
UPDATE3: Changed to cloud-based Confluence website