Healthy Respect easy to understand information on masturbation
https://www.healthyrespect.co.uk/etu/all-about-sex/masturbation/
Planet Puberty: masturbation section
https://www.planetpuberty.org.au/feeling-good/masturbation/masturbation/
Choices Support Supported Loving Toolkit: masturbation section
https://www.choicesupport.org.uk/about-us/what-we-do/supported-loving/supported-loving-toolkit/masturbation
About Masturbation for People with Intellectual Disability- For Males and Females
https://www.fpnsw.org.au/aboutmasturbation
Masturbation, Autism and Learning Disabilities (book) | Melanie Gadd
https://books.google.co.uk/books/about/Masturbation_Autism_and_Learning_Disabil.html?id=nGInEAAAQBAJ&redir_esc=y