Mr Tumble on Something Special on Cbeebies has taught my little girl a lot. We also have a book called 'My first signs ' which has been great, could see if your local library has a copy or something similar?
I did a makaton training course through the makaton website. They also have some free resources and I get emailed a sign of the week. They also offer a free trial of their membership which gives you access to lots of things. https://makaton.org/TMC/TMC/Default.aspx
As others have said watching singing hands & Mr tumble are great. Also Makaton with Lucinda. Can find all on you tube. When my son was a baby we did sing and sign classes. Not sure if they do toddler ones. But you can also do online ones. https://singandsign.co.uk/
Does he go to nursery? If not it might be worth seeing if you can get a place with the funded 15 hours after Easter. They can be a big help with speech and language delays. Local children's centres sometimes do stay & plays or speech & language training too.
@Tiffany sing and sign is brilliant it’s what they use in nursery. My son has learnt the signs for nappy, food , drink and the like from it and thier mascot Jessie cat is a big hit
We learnt a lot of Makaton from the Singing Hands YouTube channel - they have specific videos for different themes like food, days, actions etc, as well as songs which my daughter loved when she was younger. Also Mr Tumble on Something Special and he has clips on YouTube too 😊