The bed was a great deal in King size! It doesn't require a foundation because of the slats. I purchased a 10" gel foam mattress in a box from Wayfair for this bed and I love them both. However, the 10" mattress is not high enough and the comforter puddles on the floor. Its ok if you don't mind that. I would suggest purchasing a 5" foundation to go over the slats to raise the height or buy a 14" or higher mattress. You could also get away with using a queen comforter or duvet.