Have you considered a ladder that is installed on the side of the boat as an alternative? I'm not familiar with your boat but sometimes a transom could be a difficult location for mounting a ladder if it is a reverse angle or depending upon it's shape. Keep in mind that a ladder mounted on the transom can be difficult to use if there are waves in the Anchorage and the boat is pitching up and down.
There are stainless steel ladders that are removable and inserted into keys installed on the gunnels by the lifeline Gates allowing access on either side that can be easier to board.
What ever you but make certain it extends below the water a couple of rungs as it makes it so much easier to get out of the water that way.
I'm not certain about brands but an internet search will show you what is available. We got one from West Marine and have been pleased.
I think a boarding ladder should be permanently installed, not something you dig out of a locker and hang over the side when you want to go swimming.
You should also make sure the ladder can be deployed from in the water. A simple rope hanging down that you can pull to release the ladder does the job.
Depending on the shape of your transom you may have a hard time finding something "off the shelf". You may need to get something custom fabricated.
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