It really does depend on the cat, My Ash would be quite happy being a single kitty in the household, he tolerates his adopted sister fine, but he really does not care for her much.

Ash is also getting on in years and prefers just to snooze all day, and I am home all day mostly, so he is not alone all the time, so age and personality comes into it., cats are no different to humans, some like company, some donot.

My Lexie is young only 2 years old, she loves cat company, and tries so hard to be friends with Ash, so for her cat company is important I think.

I also think that kittens should be adopted in pairs, especially if you are at work all day, as they do need companionship at this young age JMHO.

If you are not ready for another cat, then leave things as they are, only you know if your kitty seems unhappy, as the saying goes "If it ain't broken why fix it"?