Eh, "book" is widely used as the unit of literature. If someone says "I wrote a book!", you don't assume that they created exactly one physical item by writing on a lot of pages and tying them together or anything.

Alternatively, if you know the type of literature, you can call it a novel or a poetry collection.

> a physical item

Not really. More like, "a container". It goes in the direction of "physical" (as opposed to the content), but it is not necessarily physical. For example, a file already is a "book".