How about this simple solution. Not expensive either. Get some teak boards or nice oak boards Cut to fit each step, Taper or round edges so they arent sharp. Then attach with 3 tube straps to each rung of your swim ladder.
I did this 12 years ago and take them off every 5 years or so to revarnish.
Here are examples, but you can get wood amywhere
Two Hole Strap by CADDY - Pipe Hangers and Clamps by Zoro Tools Industrial Supplies
Teakwood 23 1/2 Inch Boat Step
Putting steps into the boats stern will require backing plates and a lot work for the expected reward I think. They will have to sipport a lot of weight in a small area.