I've used progressive bifocals since before I got my first e-reader. The eye doctor said that I could either stop knitting, reading, and playing video games, or get bifocals.
When I had my EZ Reader I used the "medium" font, and the coolreader engine for best reading. The Nook STR I had for a while was terrible. Some of the books I had were locked into tiny, thin fonts and I couldn't read them. My Kobo mini is good. I tend to use something around size 12 to 14, and I want to say that I'm using Meyro(sp?) font. It's easy to read and has unicode characters.
Mind you, I don't see 20/20 even with glasses, so I'm not sure if you'll have my luck with lenses, or if you'll be like some of the other people in this thread.