Ground cover for run?

Hi! First time chicken owner here. I just got my first set of chicks and am in the process of building their coop and run for when they’re big enough to go outside. I’m seeking advice on the best ground cover for the the run. I excavated the footprint of the run down about 6”. Our soil is very clay-y, and my plan was to put a few inches of gravel down for drainage, and then something softer over that...I’ve read that dry wood chips are a good option, but am not sure where to get those locally? Any other suggestions?