As I am getting back to scrolling I have been using 5/16 plywood I think it is called luan plywood or door skins its relatively inexpensive.
I have tried common pine but it is pain to cut around knots so usually use clear pine, popular is also a good choice.
I get either 3/4 or 1-1/2 of the wood and rip it down to thickness size on my table saw, don't forget you lose about 1/4" for blade width