The singapuran is the smallest breed among the domesticated cats, however I think it's quite expensive...
Slim cats with short fur such as rex and siamese tend to appear smaller than longhaired and more cobby cats such as the persian.
Don't forget to think about the temper. Do you want a cat that'll be playful, social, independant, quick to learn etc?
And since the female you already have is spayed, the sex of the new cat doesn't really matter. Just remember that spayed/neutered cats often are submissive to fertile cats. And older cats can be a little bit "touchy" about new cats.
Slim cats with short fur such as rex and siamese tend to appear smaller than longhaired and more cobby cats such as the persian.
Don't forget to think about the temper. Do you want a cat that'll be playful, social, independant, quick to learn etc?
And since the female you already have is spayed, the sex of the new cat doesn't really matter. Just remember that spayed/neutered cats often are submissive to fertile cats. And older cats can be a little bit "touchy" about new cats.