I'm getting a lot of use out of my ancient Sony DPT-S1 for this purpose. It has a huge screen but is very light and well-balanced so holding it for long periods is not a problem for me, compared to holding a similarly-sized lcd tablet. I've converted most of my epub ebooks to pdf (thank you Calibre) just so I can enjoy reading them on this device.
I got one too and they really rock! I read papers on them mostly and the odd text book. I had a Kindle fire reading novels but have last it recently. I'll maybe take a sieve or of your book (ha!) and try converting everything to PDF, but I really like the built in dictionary on kindles. just wish The DPT-S1 was open to writing your own apps for, I would have done it by now.
That means an e-ink device the size of the pages. So probably A4. A device of 21x30cm. (8.2x11.7inches). That is huge. Equivalent of the largest iPad.