I know you asked for a backlit device, but there are not that many at this time.
You mention portability for the reader and the light. I have read many people having good things to say about the PRS-300 with the Sony cover with light attached.
Model number: PRSA-CL3 It's still has a small footprint and the light is always available. I can not vouch for the brightness of the light, but it does address the portability issue.