I've used these in the past.
They are cheap, sturdy, and available at Boat jumbles most of the time.
I can't find an ebay UK source at the moment, but believe they sell them at the Port Solent Marine superstore
https://www.ebay.co.uk/itm/263929353...MAAOSwIwpf7C~j
I ended up Cutting and welding a normal ladder for my Ocean to make it narrower.
It's survived years of abuse.