Panel assemblies designed and configured to be installed into cushioned and other occupant-supporting furniture to increase the support provided to one or more occupants of the furniture. Each panel assembly is composed of interconnecting components, such as panels and slats. The components are interconnected in any one or more of a variety of manners, including side-to-side, overlapped, and stacked, and combinations thereof. Each panel assembly can be made from one or more kits of components that can be provided along with instructions, such as assembly instructions and installation instructions.