If it's blocking your writing... Explain this exact problem in a preface and move on while an answer (hopefully) percolates in the background.
I'm a big nerd and affectionately refer to my family members as "units" in a deliberately ironic way. E.g. my children are childunit01..03 and wifeunit01. This is probably a useless anecdote though.
The point though is that a physical individual is the unit of interaction for people, even if that physical individual houses multiple people or a person that doesn't conform to the physical representation. It's also the unit of interaction with the world, or interface if you will.
I'm also a big sci-fi nerd, so intelligent non-human interactions are a big part of the media I consume. Many authors deal with the same problem. You could look there for inspiration.
Of the top of my head "agent" (as in agency) seems like a good candidate. Everything alive had some degree of agency, humans probably have the highest degree.