I have made a lot of fidget mats for the Alzheimers ward at the local nursing home. All were well received. Size is usually the size of a large placemat. Mermaid made lovely ones and should give you some ideas. Use bright colors--not dark. Sew zippers and put a tiny ribbon on for a pull. different types of fabric squares--velour, terrycloth, minky, anything that is textured for a feeling sensation. Pockets, make sure they're hand sized, ribbons work well. Make sure everythings is sewn down.