Extra Firm Mattresses / Extra Firm Futon Mattresses
Amazon.co.jp: New Japan Mail Order EX Mattress, King Size, 70.9 x 78.7 inches (180 x 200 cm), Air Press, Body Pressure Dispersion, High Resilience, Firm, Firm, Futon Mattress, Overlay, Gap Gap Protection
Amazon.co.jp: Japanese Futon Mattresses: Home & Kitchen