Given your parameters, I highly suggest a cat, fish or both. When programming, I've found that my companion of a cat (two tiger striped male and female, 6 yrs and 4 yrs old) are fantastic mood enhancers, that is when they're not crying like babies for food. Barely any maintenance when compared to a dog, but the only downside for me personally is cleaning the litter box (could always get the automatic litter box that cleans itself), but it's extremely necessary if you expect your pet to be clean, which translates to a more hygienic living space for you too.
Fish are also great mood enhancers but can be a bit more work in my opinion than cats, at least for the initial setup and routine tank cleaning. But overall - just sitting back, reflecting on some code while staring at the fish tank has worked wonders for me producing small epiphanies.
The automatic litter boxes aren't that much better, in my experience. Sure, some days you won't have to pay attention at all, but every few days you'll have to completely take it apart and clean it, because the mechanism is easily clogged. This was true both with a straight rake box and a circular rotating pan, but maybe some brand has got this right by now (it's been a few years).
You could always teach your cats how to defecate in the toilet. (don't teach them how to flush though as they will continually flush to the chagrin of your water bill and mother nature.)
The latter part of your post is largely why we didn't go with this option, although it would be nice if they could take care of their waste themselves.
Not all at the same time, I grew up with cats, dogs, iguanas, fish, ferrets, hamsters and rabbits. By far for me cats have been the most worthwhile investment. Dealing with the small inconvenience of the litter box is something I shouldn't complain about since simply having my cats around for companionship has paid off such valuable dividends.
Fish are also great mood enhancers but can be a bit more work in my opinion than cats, at least for the initial setup and routine tank cleaning. But overall - just sitting back, reflecting on some code while staring at the fish tank has worked wonders for me producing small epiphanies.