You say sensing is lived, but that Si is something deeper than lived experience. It is something collective. This is Ni not Si. Sensing is experienced by the senses and what you explain is a psychological phenomenon that is divorced from direct sensory experience, i.e. intuition.
By your definitions of Si and Ni I can't really see how the two are all that different.
I'm not sure how the sensation of comfort is a shared primordial experience, sometimes a chair is uncomfortable and it makes your ass numb nothing really all that deep and unconscious about it. Or I suppose another example is when an Si ego walks into a room and comments on the harsh lighting, is it really unconscious? No.
TLDR: You need sensations to engage with your sensing functions, this is only done through direct physical experience, the concept of "experience" is historical in nature (past,present,future), Si relies on past experience.