Don't know if it's too late, or if you already bought it, but that DS Lite case that looks like a sock, which comes with Mario skins (and is free at CC w/purchase of a Lite) is a good case.
I just keep my Lite inside the covering that it was packaged in, and slide it down into that sock thing. Nice cushion and protection without being really bulky. CC also has another case for the regular DS that's really good for carrying games and accessories.
Annnd, for the record, I'm always late to the party.. lol