Does the Amish flat arm futon frame come with a mattress?

No, the Amish Flat Arm Futon Frame is sold as a frame only; futon mattresses, covers, and pillows are all sold separately. Compatible pairings include the Pure Comfort Natural Cotton Mattress, Teddy Bear Wool Mattress, and Eco Pure Wool Futon Mattress, all available directly on The Futon Shop's website.