It's fine to sit either on a cushion on the floor or on a chair.
Once you've picked your spot, you need to choose your seat. It's fine to sit either on a cushion on the floor or on a chair. If you choose a cushion you can use one designed for meditation practice like a zafu or gomden or you can use a folded up blanket or some other kind of cushion or low bench. The point is to have a seat that is stable and not wiggling around.