A tower assembly for a wind turbine includes a tower and a freestanding internal tower structure assembly. The tower has a tower wall defining an inner surface and an outer surface separated by a tower wall thickness, with the inner surface defining a tower interior. The internal tower structure assembly is positioned within the tower interior. The tower structure assembly includes a plurality of stackable support structures configured to support one or more internal tower components. Further, the tower structure assembly is freestanding within the tower interior.