I hope you don't mind if I confuse the issue a little further. I love my Sony Reader. I read more with it than I did with my Palm devices. But if you are looking for something that has a narrower screen, a refurbished monochrome Palm might be a good choice.
The monochrome Palms use two AAA batteries which are available in rechargables or off-the-shelf alkalines. They are always available. The mono screen gives good contrast without backlighting so it is easy on the eyes. The font size can be quite large.
I bought my Palm M125 as a replacement for an older unit. I found it refurbished for US$30. It is perfect. I usually carry it with Me, as it is more portable than my Sony Reader. I like eReader. It offers reverse video backlighting which is great. I use Plucker to download news sites so I always have some casual reading available. In addition, I carry quite a few books on the Palm. It had an SD card, so I can carry as much on it as I can on my Sony Reader.
It is not an expensive purchase, so it makes a good first step into the world of e-books.
See
here and
here and
here.