Yes, a thing would be something we perceive as a thing. A lattice of carbon atoms would be a thing, but a single random atom wouldn't be a thing, but a simple random atom.
So a thing would indeed be a body or object [in its widest sense].
This means that there are no non-material things.
An object of the mind is a mirage. That doesn't mean a mirage can't have power or excert influence, but in- and of itself has no substance.
I believe that metaphysics, while playing an important role in human evolution, acts as a justification for the 'what-if?" questions. By waxing eloquently about these topics one conveniently evades the question, "Is what I believe actually true or wishful thinking?".