There must be puffyer cotton batting out there but oh what a problem to quilt close though that it would not shift in both use and washing. I don't know where the "advisor" in the store has been. That, to me is not an answer. She must have been quilting 12" apart on her polyester batting or used one that was not made without falling apart. Advice like you got in the store just makes me shake my head.
Cotton will flatten in time just laying on the bed. So the advice you got above about finding out what is meant by "puffy" is a good one. Puffy to you may be different than to him. Then if he wants real puffy consider the difficulty in quilting it if you do use one of the thicker battings which really have to be tied and not quilted.