Change email associated to icloud

So I've been on an iphone for several years and set it up with my gmail as the user name. For personal reasons i am trying to migrate away from gmail. I created an @icloud account today and when i try to change it from within icloud.com i am getting an error " You can only add the @icloud.com address that is already on file in your account."

Then when i try to add the @icloud email under "reachable at" i get this error " This email address is not available. Choose a different address"

I was able to add the @icloud email under accounts so i can send and receive email from the device, however i want the @icloud email to be the default email i use to log into my icloud.com account so i can dump gmail.

any ideas?