Do you need more motivation to finish things related to bugs and feature requests? You could use some governance model for user feedback. Direct user feedback can grow your motivation, you dont need a product owner for that otherwise your backlog will grow quite fast I think.
Discussion
Its not so much motivation, but organizing and prioritizing things. there are so many views in the app that need to be redesigned and made simpler and its hard to know what should be done first. or maybe I should focus solely on bugs?
Let your userbase vote on the items on the backlog what they would like to see finished first?
15 years ago I remember I was using the tool UserVoice for this kind of curation.