Any sound board material will work. To me, copper is unforgiving when running. You either good or your bad. That said, copper playing surfaces creates a higher pitch, almost a "screechy" sound. With that, I prefer to utilize a wooden sound board or slate under my copper to bring the pitch down a bit and make it a bit more forgiving. It's all preference. You'll have to make a few different combinations and find what sounds best to you.
Jeff