We made "sitting pillows" with 3rd grade by making rectangle inner liners out of old sheets and filled them loosely with buckwheat hulls and sewed them shut. Each child brought fabric from home and helped cut and sew pillow cases that could be removed and washed when needed. The children loved any/all parts of the participation and had their special pillow to sit on all year. The hulls made them nice and squishy for floor sitting, and as they came in huge bags, must not be very expensive. They could use tees, or even old shirts, curtains, etc. as the outer covering; just sew up the openings other than the bottom.