If you are already using Calibre, then converting your ebooks to whatever format is best will be really easy. For the DRMed LIT ebooks, you need a keys file from a Windows PC but it should then be possible to "downconvert" them to DRM-free. Leave them as LIT, and let Calibre convert them for you.
I think it is possible to use the EZ Reader with your left hand only. It has page turn keys on the left and I normally use it left handed. You will need to use the number keys on the bottom for menu navigation though, and I use my right hand for this. It might be worth waiting for the
BeBook Mini, or the
EZ Reader "Pocket PRO", with a similar key layout but smaller overall and with a 5" screen. There are other nice looking 5" devices in the pipeline, see
PocketBook 360° final design and
New Device: Bookeen Opus. How they will work in practice is as yet unknown,
I am less sure about using Kindle with the left hand only, because the K1 has a right-side scroll wheel and the K2 has a right-side 5-way pointer.