i just use my 55cm fit ball. or exercise swiss ball. everybody calls it something different .
it is quiet, but you have to realize when you stand up it may roll some, so you HAVE to check to make sure it is under your toosh before sitting. also it doesn't move as fluidly as a roller stool might. that's just a couple of cons, but i love it and use it all the time.
a good one costs about $20 and sitting on the ball puts less pressure on your spine than sitting on a chair. you can use it whether you have carpeted or hard floors... and you can use it between clients to stretch out lumbar and thoracic spine and (i love this) pecs, just balance on it with arms hanging out to the side. plus it's a good tool for showing clients ways to use it in the office for sitting and STRETCHING. those are some pros.
i also use it when seated at the computer.