Can you suggest an e-reader to purchase?

I looked at a Sony Reader PRS300RC which is under $150. But it is only about 5” tall. It was suggested I buy the one from Barnes & Noble, but they are over $250. When I read a book it is either large print or I take off my glasses to see better-so I’m concerned about the 5” size, but I know you can increase font size; also concerned about the light/dark background interferring with sight.

The program you need on your computer to be able to download books onto the reader-is it safe? I only have internet at the office and need advice before I go and ask if I can.