I've seen some particle board baseboards warp over time. Plywood may be more rigid. Rather than using really thick plywood, consider two layers of relatively thin plywood separated by a properly designed and glued pattern of wood strips to function much like an I-beam. It can be stiffer than a solid baseboard of equal weight, but thicker.

If the base of the column has a small area of contact with the baseboard, it can compress the wood fibers and cause the column to tilt slightly. A metal plate to distribute the pressure can reduce this.