Recommendations for a effective vapouriser sort.

Our youngest, Isaac, suffered from respiratory problems at birth, and spent a while in the ICU, although fine now he seems very subseptible to getting chesty coughs.
I am thinking a vapouriser might help, there are so many different types and opinions on the web as to which is best that I am a little unsure what to get.

I am erring towards a simple cool mist type, anybody out there got experience of a good model/brand?

K