go all out and use 1x10 or 1x12 pine boards and use a router or table saw with a dado blade to cut a rabbet on the edges to overlap the board below it leaving a small gap. Do a google search and you will find both ways.

We just took out a bunch of shelving done with 1x10 boards that are 12' long so I will end up doing a couple of walls using that and a rabbet