Either yarrow or cayenne will warm things up and both are good expectorants.
Maybe try the mullein and elecampane separately and see if he can tell which he doesn’t like.
Maybe try the good ol Peppermint, Yarrow Elder combo.
Licorice is a good expectorant as well and may be soothing and calm whatever he’s feeling from the Mullein/elecampane.
Patrick
Don't use herbs or combine herbs with medications or use them during lactation or pregnancy without talking with your healthcare provider.