I need to identify a song from a commercial

Does anyone know the diamond commercial that has the couple lying in bed, the man sneaks out of bed to get his wife a beautiful diamond necklace...well the song that is playing is what I want to know. Which song, which artist, what album is it on? The lyrics I can remember are...I want to tell you that I love you, that I'm always thinking of you, thinking of you...But I can't find the right words...etc. Please help me! It sounds to me like Diana Krall.

You talk of this commercial?: YouTube - Cat Stevens cover "How Can I Tell You" diamond tv commercial

That one is Chan Marshall (her stage name is Cat Power), and she is covering a song called 'How can I tell you' (originally performed by Cat Stevens).