If you live in an apartment or rent a flat, your landlord might not allow pets, or if they do, maybe only certain kinds. These are going to be ones that don't create a lot of mess or smell. For that reason, ferrets are not a good idea. If you live in a house without a garden, then you shouldn't get chicken either, because they need to be outside so they can pack and scratch.
Small rodents such as hamsters rats are a good choice, as they don't need a huge amount of space. If you want something bigger, then unlike a dog that needs to be taken out for walks, and should have a garden to run around in, a cat is more independent, and can find its own territory outside your small living space.