Anudder one?

It's up to you, but it seems to me that so many of the behavioral problems people post about seem to come from having more than one cat in the house. If your cat is happy, healthy and well behaved then why mess with it?

Of course it would be great if you added another one and the two of them got along with no issues, but there's really no guarantee that will happen. Cats don't really like change.

My standard answer to this question is only get another cat if you want one, not because you think your current cat needs one. Cats do just fine as only 'children', if a second cat is brought in they may or may not become best buds. If there is an extended period of tension...you're the one that is going to be dealing with the collateral damage (e.g someone peeing outside the box) and if you're not completely committed to the idea of two cats then you're going to get frustrated with the situation.