I have a small (8' x 7') room with 2 exterior cinder block walls. I live in a seasonal climate that is both hot and cold. I want to put up drywall. What is the best way to do that given that:

1. I want the room to be reasonably well insulated
2. I don't want to increase the thickness of the walls too much.

Should I just frame out the walls with 2x4's and use batt insulation, or should I use foam board instead?

Thanks!