Hi there, I switched your primary domain to teachingtea.wordpress.com under Store > Domains so that your site appears in the meantime (it's private, so it only appears to you).
I'm not quite sure what your end goal is -- are you planning to move away from WordPress.com and use third-party hosting? In this case, rather than a Domain Mapping upgrade, what would be useful is a Site Redirect (check out the support article at the link to determine if it's right for you).