For use under a latex mattress, we have been using this Spindle foundation for about 10 years. We changed our bed frame and no longer need the foundation. The foundation is two XL Twins because the boxes do not collapse. The slats do (hence the bunching). Unfortunately, one of the support boards broke (see third picture) but could be replaced. Priority given to anyone who wants both but will separate given one is damaged. See here for the original product;