I am not convinced by arguments for Sir Karl Popper's three worlds model of existence. Similar to what TheAncientGreek said, I am not convinced mental objects exist. But I suggest what you and EY are writing about, Popper wrote about in the 1970s.
David could benefit from reading Chambers The Conscious Mind , if he has not. Chalmers thinks consciousness supervenes on information processing, but his model is dualistic. David might want to avoid that.
Overview
Tentative Lemmas
Likely Complications