I don't think there are Any ink readers with Backlights. They are front lights. That being said Kobo does the ebub format which is what the Nooks use. Amazon don't do epub. They use Mobi & a few others.
There is a Fire Tablet on amazon that 6" great for sticking in a pocket. It has back light 8 gig of space 8 hours of reading you can Side load Kobo Nook and a few other apps that does epub. Hope this helps