I agree with Warm Wishes, I agree with lap quilt size. I use fleece for a backing and make my final dimensions just under 60" wide and 72" long.
You could also go with something scrappy -- maybe check the Moda bakeshop website. People seemed to think scrappy means a lot more work and they are impressed by that, but if you keep the overall pattern simple, might not be too bad...
Good luck and keep us posted!