Argh. I had written a whole response, hit the wrong key, and everything disappeared.
In a nutshell, how wonderful that Smudge has turned all of you into cat lovers!
As Marcia said, there's just no way to tell what will happen between two cats. Fostering could be a good solution for you. Many shelters have foster-to-adopt programs, or have some stipulation on the adoption contract that if things don't work out, you will surrender the kitty back to them. I'm also looking for a kitty playmate and am thinking about fostering to adopt.
Most, if not all, of the people on this forum would do everything possible to avoid rehoming. But rehoming is not a dirty word, and is sometimes in the best interests of everyone, including the cat being rehomed. It's situations where a cat is surrendered for what appears to be frivolous reasons that create such a negative view of rehoming.
The kitty I've been eyeing was surrendered, after 2 weeks, for being unfriendly. In that municipality, owner surrendered animals are the first to be euthanized.
That kind of thing bothers me, since 2 weeks is not enough time to figure anything out, and unfriendly is not, in my opinion, a good reason - especially when the woman who runs the shelter says the kitty is an absolute sweetheart and loves to snuggle. She's just timid and needed a little more time to feel comfortable.
But sometimes rehoming is necessary, and no one should feel bad about rehoming when it's clear that things are just not going to work out. I hope you won't be in that situation though, and that you'll find another perfect kitty to complement Smudge!
(And I hope the same thing for myself!)