Some people like keeping a pet as their friend. Live in apartment alone must need friend too. The pet also make your apartment colorful.
Unfortunately, the spaces in small apartement are limited. We cannot care big pets in small apartment. It will make your room narrower. The pet also could make some trouble in your small apartment like feces, food residue, and cage. The pet also bored with small spaces. Pet such like cat and dog need large spaces for playing. Both pet like running. They will be sick live in narrow area.
The small apartment owners should consider little pet for their pet. I think little bird such as canary is good for small apartment. You can feed them once a day. Clean the cage at least once every two days.
Alternatively, you can care small rodent like hamsters, guinea pig and mouse. Unfortunately, this pet could be stinky. The urine and feces is very stinky. You should diligent to clean the cage.
I advice you keep a freshwater aquarium. You do not have waste so may times. The keeping is easy and cheap. You can give the food once a day. The price of pet is also cheap. You can buy a tiger tetra only $
Since your apartment is narrow, you should buy small aquarium or at most 20-gallon tanks. Put the tanks with small fish like neon, tetra, goldfish, dwarf catfish and dwarf cichlids. Do not care longer fish that could make you difficult. Star with gold fish because it is easy.
Clean the tank routine. The tanks should clean from algae and food residue. Replace the water 20% once a week.
Before buying a pet, you should consider money and family member. You do not have own a pet, if you have no money. Is there any family allergic? Some people cannot stand with certain animal. Consider your jobs too. If you are a busy man and there is no one helps you, you should not care any pets.