Let me try again. There are three possibilities that can be stated about consciousness:
1) It's a material thing.
2) It's a non-material thing.
3) It's not a thing.
But #1 can't be true or we'd be able to create a test to determine whether or not it was present, at least in thought-experiment form. And #2 can't be true, either, because there are no non-material things (if there are, we're stuck in supernatural-land). So that leaves #3: it's not a thing at all.
But what isn't a thing? Well, what IS a thing? A thing is another (and less formal) word for a phenomenon: something that can, in potential, be observed. And that means it's a part of the universe -- not the whole of the universe, but a part of it. So consciousness can't be a part of the universe, because it isn't a thing.
If something isn't part of the universe, there are only two possibilities: it's the whole universe, or it doesn't exist. But consciousness
does exist; as you say, we can verify that subjectively. So consciousness must be the whole universe.
Here's another way to approach it. Assume,
arguendo, that you and I are both conscious and that my consciousness is separate from yours. Since we agree there are no non-material things, it must therefore be a material thing, maybe a function of the brain. But if that's the case, then I should be able to see, or otherwise verify objectively, your consciousness (although it makes sense that I couldn't verify my own for the same reason as an eye can't see itself). But I can't. Therefore the premise must be untrue.