Can cats do just fine without another cat companion? Sure, as long as they get plenty of interaction with their human companions, but a cat with a friend is likely to be just as social with humans while still enjoying feline companionship.
There really isn’t any one right or wrong answer. If your cat prefers to be alone, there is no reason to fix what isn’t broken, but if you find yourself longing for another cat in your family, you shouldn’t hold off just because someone says cats should be alone.
If you decide to get another cat, simply take your time to allow both cats to get to know one another. Don’t pressure them or try to force them to be friends – they will figure it out on their own, and in their own time.
Cats can be solitary, but just like their distant cousins the lions, they get along great in a “pride” as well. There is no one size fits all answer, because cats are unique and have their own individual tastes and preferences.