These are common options but may feel different per manufacturer.
Peach skin: smooth polyester. No stretch. Least expensive option.
2-way tricot: stretchy. A lot of people on the /dakimakura/ reddit say this is the best, but I don't personally like the samples I have ordered. It's heavy and feels like the material that cheap halloween clothes are made of, and everybody says it tears easily too.
Velvet: ?