For a restricted field of view, a small device with many pixels may be your best bet. The Nokia 770 is a good example. See
Visual Tour of FBReader on a Pepper Pad 3 for many screenshots. These are on a PepperPad but the Nokia has the same number of pixels (800x480) on a smaller screen (4.2" vs 7" diagonally). With FBReader, you have very fine control over the text on the screen including wide margins if you need them. A downside (some would say upside, in any case a feature) of the Nokia, and FBReader, is that it can only read non-DRM e-books. If it is legal where you live, one solution to this is to buy encrypted Microsoft Reader .LIT files and then explode them to non-encrypted .OEB html files - which FBReader handles nicely. The same approach (start with .LIT) may be necessary if you need to reformat a DRM book to be optimally viewable on the Sony Reader, and I think this kind of "fair use" is even legal in the US.
The Nokia 770 isn't the only candidate with a LCD screen - a high res. PDA might work well and will usually support MobiPocket Reader and other good e-book reading software.