Business Insider

The Firmest, Flattest, Healthiest Way to Sleep—At Least in the Western Hemisphere: This 2-sided mattress by Brooklyn Bedding is the only truly firm one I've found since returning from Asia — if 'firm' is never firm enough for you, this one might actually work. [T]he sleep on the "ultra-firm" side of the Plank was just too good (the brand calls it a 12/10 on the firmness scale, while the regular "firm" is rated as 10/10)...Short of sleeping on a hardwood floor, this is the most supportive and corrective mattress I've found in my trials of over half a dozen ‘bed-in-a-box’ mattresses.”