A cat. They really are the ultimate low-maintenance pet, and they give back a lot more pleasure than goldfish. Provided you have access to a garden, you can install a magnetic cat flap, so your cat can come and go freely, and you never have to interact with his poo. Feed him dry food and water (water's better for him, and good quality dry food is perfectly healthy, too). Neither of these smell, attract flies or go off.
If you forget to feed your pet, he will make a racket outside the food cupboard until you remember. You can even go away for a couple of days without putting him in a cattery provided the cat door's working and you put down plenty of dry food and water.
Like all pets, they get expensive when they get sick or injured, so pet insurance is a good idea.
If that seems like too much trouble, a tamagotchi is definitely the best choice.
Oops - sorry. I see you have no garden. Why not just move?