Something to add is that all previous usernames will not become available they are permanently associated with your account so there no hope of getting a username already taken. I asked Sony after the name I wanted so taken but I couldn't find a user with it so asked when the old ones would become available after switching as was told they will never become available. The tweet I was sent back:
https://twitter.com/AskPS_UK/status/1116321355249614848