Related to your remarks about pure consciousness and the object of which it is being aware, who or what is the observer?
Some of the people I work with have Dissociative Identity Disorder (DID) (formerly called Multiple Personality Disorder.) , and many people experience dissociative states. People with DID have compartmentalized (in any number of ways and configurations) both the conscious and the unconscious. There is clearly one body, one human entity, sitting in the chair opposite me. That one entity experiences itself as being more than one human entity, sometimes simultaneously, and sometimes not, and with various degrees of "co-consciousness" of the other identity fragments, depending on the completeness of compartmentalization. Assorted "personalities" with conscious awareness of other of the "personalities" may have the perception of sharing a body with other 'people', other of the co-conscious "personalities" may believe they inhabit a separate body, even to the point of attempting to physically kill other of the personalities, unable to recognize it as an attempted suicidal act. (Rude awakening when that happens!)
"I think, therefore I am" is not existentially confirming when one mind is fragmented such that there is the subjective experience of more than one "I" accompanied by belief based on that subjective experience that the separate "I"s are truly separate beings, whether they inhabit the same physical body or not.