You did not understand Descartes then.
Je pense donc je suis = I think therefore I am
The 'I' is not the body, the habits of descartes because all that is perceptions also.
The 'I' that Descartes talk is consciousness itself.
But he believed there was many 'I' consciousness different than his 'I', different souls.
But he failed to justify this. He tried with the assumption of the existence of a good god that created a world arround with different soul and give human the ability to know the world.
Also, when he was using the word thinking (penser in french) he was referring to consciousness.
so he was only entitled to say: there is consciousness!
I have read Descartes but I disagree with your interpretation. He was only entitled to conclude that there "is thinking". Thinking is what a brain does.
What on earth has "penser", to think, got to do with consciousness other than in the sense that I may be conscious that I am thinking. The terms are not interchangeable.