I'd approach it much like an I Spy quilt, made with blocks. Every block doesn't need something to do. The rest of the blocks could be colourful and with I Spy material for visual stimulation. This could include photos transferred to the fabric if you are making it specific to someone you have access to pictures.
Some fabrics ... corduroy, velvet, burlap, polar fleece (perhaps the backing?), velvacord, fur fabric, suede, leather, pleather, trims, chenille, flannelette, clear plastic (window!), plastic that gives a mirror effect), fine wool, coarse wool, denim, sparkly, shiny, etc. Be sure to check out decorator fabrics for some different textures. What would be like sandpaper??
Some fidgets ... zippers, velcro, snaps, rivets, cording, shoelaces to tie up, buttons, pockets with hidden items, roping, trims, coarse lace, ribbons, braids, hooks and loops, etc. Keep an open eye in your notions department as there will be lots more! Think of our different quilting techniques that provide fidgetable (new word!!) items.
Some pocket items (have them on a "leash" and permanently anchored inside, so they don't fall and disappear) ... flashlight, small toys/dolls, other textures such as a silk scarf, an embroidered/lace hankie, mylar foil for crinkly-crackly sound, a knitted mitten, something crocheted (a doily? a granny square?), etc. Cut off some pockets from jeans and sew them in as patches.
I know some of what I have said above are duplications, though I'm not going back to check which they are!
ITA with others, if this is for someone wheelchair bound, consider the apron, or perhaps a tie or velcro to attach to the wheelchair. Also, safety needs to be considered re any of the more loose or longer items.
My Mother had alzheimers, so I know the sorrows and how difficult this time is for family and loved ones. In a lot of ways, it is more difficult for the family than the one inflicted.
Bless you, 29Cathie, for taking on this opportunity!
I'll look forward to seeing what you create.