Terrarium pebbles- will just any do?

I am making an enclosed terrarium, and I have read that I need to put a layer of pebbles on the bottom. Now, some places say to use coarse pebbles or sand, some just say pebbles, and some say things like wood chips or gl work best. So what should I use? I've seen smooth decorative rocks at target, which I like, but I'm not sure if those will work. I'd rather not use fish tank gravel. Other than that, I have no ideas as to how and where to obtain pebbles for my terrarium. Also, there are no pebbles in my yard or anything, so I have to buy these pebbles. What should I use?