LOVE this thread - but sooo not ready to narrow it down to a single book. Need to contemplate before answering.

I did however want to give a plug for some in-the-middle-of-the-night-book-reading aids: get yourself a clip on book light and (best one of all) a book beanbag. It's like a pyramid-shaped pillow with a ledge and a thing that holds your book open so you can read hands free! (I sooooo needed one of these when I was bfing). It's squishy too so you can adapt it if you're lying down reading.