You are entering the question assuming your experience is a single point. But that feeling and thought only exists because there is the emergent abstraction of the state of your brain having that feeling and thought. You perceive a singular point of existence because that is the only way your existence can be perceived by the brain you have. That is the state of your brain and you cannot perceive it as separated because the state does not represent it that way. Anything else would require different state.
Remember, we've established that your "soul" cannot change the system, it's an observer. So even if there was no underlying perception of experience and you were a philosophical zombie (so-to-say), you would be saying the same exact thing and "feeling" that same individualism despite that not being true. The ethereal you isn't saying these things, the physical brain is. Your self awareness about your own perception is false, the state of your brain interprets it's own self awareness this way and therefore that's how you perceive it as an ethereal soul. Not the other way around.
But if you, say, take hard drugs, the state of that system can be different and you may not feel a singular perception point. You may feel like a billion neurons coordinating for a moment.
So you think you are a single thing because you have a human ego and your biological brain evolved to think of itself as a single construct with an individual perception.
Your trouble arises from the fact that you're still stuck in the mindset that you have a soul that can affect your thoughts. But that's backwards. Your brain cannot actually understand anything about its observer. The brain is programmed to self-reflect like this and therefore an observer must feel themselves self-reflect in the same way.
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WRT combinatorial complexity, yes. Every combination of everything would have its own "perception" of existence in my philosophy. Because it's entirely emergent, it only makes sense to me that this underlying perception one might call a soul would be more accurately described as just... The nature of existence itself.
"I" exist because my brain exists. I cannot not exist because my brain does exists. That state is real. It has to be this way.
In that same way, if an atom exists, that atom exists. It must. It wouldn't experience existence in any fathomable way, but it still would. And so to would a tree or any colony or chair.
Your example of you and the chair is poor, because you are experiencing the existence of your brain. You are not experiencing the existence of individual parts of your brain or the chair and you as one thing, because your brain does not include that state and therefore the experience cannot be interpreted by a physical thing.
I hope all of that makes sense... But ultimately it's just something that has to "click" or you won't understand.
Anyway, lovely chat. :)