I note you are asking about a step rather than necessarily a ladder.
I have a plastic stirrup.
I don't use the deck
attachment, but just tie to one of the stanchions. When underway just flop it onto the deck
Another solution I saw was a stirrup fabricated by another cruiser. This was 2 pieces of foam pool noodle tied together with a piece of conduit through each, and then the supporting rope
threaded through that. The conduit provided sufficient shape and strength, and the foam was soft on the feet.