'The Only Thing That Matters Is Christmas With You' is not included at the Good Luck Charlie, It's Christmas! Soundtrack. However, we think that it was Bridgit Mendler who sang it, as if you listen to her song I'm Gonna Run To You which was also featured on the series. You can notice the similarity of the voice.
Bridgit Claire Mendler played the lead role of Teddy Duncan on the Disney Channel Original Series Good Luck Charlie from 2010-2014. Her credits as a singer include her singing the theme song for the series, entitled Hang In There Baby.
Currently she is hard at work on the show Undatable, working on new tunes, and they are on the way for fans to hear soon!
Tip! To find the latest updates about Bridgit Mendler, just visit her Facebook page or follow her on Twitter @bridgitmendler.