Hi! France, how wonderful! Look at your machine, does it say 110/220 volts, 50/60 hz? If it does then it will automatically convert and all you need is an adapter so that you can plug it into the wall. No converter needed. If it doesn't, then you need a converter that is large enough to convert it from a 110 to a 220 and an adapter for the plug. The size you need depends on the wattage used by your machine. Most likely if your nebulizer is a newer model, say within the last couple of years it is probably dual voltage. If in doubt, call the manufacturer and ask them directly. I did this for my daughter's machine when I could not read the voltage on it.
Have a great trip! France is beautiful, and despite the widespread belief that the french are rude, they are not. We spent alot of time in France while stationed in Germany and never encountered a bad experience while touring, shopping, dining, camping or simply asking directions.