when i was a wee girl scout we made our own cushions out of (easily wipeable!) plasticy picnic table covering sort of fabric. longish rectangle, folded in half. someone (maybe us, maybe an adult before we got there, i forget) punched holes about an inch or so apart around the 3 open sides. we stuffed them with some layers of (quilt batting? foam? it was a long time ago) and we sewed them up with plastic needles and yarn. you might be able to make it more eco-friendly by salvaging supplies - i'm sure you could get some plastic needles and yarn donated, maybe creative reuse pgh has fabric and foam/batting? i had mine for years, used to sit on it and watch gummi bears
i might have some books you can have. i'll look around.