Everyone has their favorite place to read. For some people it's a chair or in bed. Me, I tend to stretch out on the floor on my stomach with the book spread in front of me. This is how I do most of my reading, though I occasionally sit on the couch or lie on my back in bed for reading. I've always been kind of a floor person. At parties and family gatherings, when seating is always at a premium, I never mind sitting cross legged on the floor. Part of this may be my couple of decades in martial arts. You spend a lot of time in class and at seminars sitting on the floor. But I suspect it's mostly just personal preference. I often sit on the floor with my back against the couch when I watch TV or play video games. In fact I mostly bought my couch for the comfort of visitors. I'm usually at my desk or in the floor.
But for reading, I definitely prefer the floor position. Even when researching, I can spread a bunch of books within reach and switch back and forth, sliding one book into the place of another. Maybe if I had a bigger desk I might do more of my research work sitting up. But I doubt it.
As a final note, whenever the phone rings or I need to get up quickly I do so in one of two ways. I either do a push-up and bring my leg up to my chest so that I can stand straight up, or I roll to my back and come up in the ju-jitsu base position, which is the best way to get up in a fight. Old habits die hard.