Plywood is indeed a good board, the screw holds really well but it's expensive, another option is OSB, a bit splintery to handle but it holds well too, though not as well. Avoid particle board if you can, it tends to crumble if you remove the screw once, making it difficult to secure it in the same place again. Otherwise, you can use råspont, takes a bit longer to set up, but it holds really well indeed.
Often, as is common with drywall, when you intend to mount something heavy, you add reinforcement on the backside with a scrap piece of wood-based material you happen to have on hand (OSB, chipboard, planks, whatever). Take the opportunity to create a neat solution for hiding cables inside the wall while you're at it.