Clue: 'Coochy-coo' etc: additional vacuous expressions embraced by yours truly (9)
Answer: MOTHERESE
Explanation: Definition: 'Coochy-coo' etc
An envelope ('embraced by') of OTHER ('additional') plus ES ('vacuous **E**xpression**S**') in ME ('yours truly'). I could not find MOTHERESE in my Chambers, but is is in Collins online, and in Wikipedia, under baby talk.