You use helium. Helium is an inert gas. But it's expensive. I'm afraid you can't accept it.

I estimate that you have to hang two kilograms of things, and helium costs at least 300 yuan.

You can find a wedding company or a etiquette company and ask them to fill you with helium. This is easier to find.

Remember to drag things with a rope below, or they will fly.

good luck