https://www.amazon.com/Deluxe-Studio-Style-Yoga-Meditation/dp/B00M793WZM/ref=sr_1_26?ie=UTF8&qid=1498142561&sr=8-26&keywords=Crescent%2Bmeditation&th=1 do i need to get a seperate ground mat thingy filled with buck or cotton? as or just the cushion is good enough to hold me away from pain?