Hi Denise,
From my experience, there are really very few cats who absolutely require being
the "only cat." Many are slow to accept the interloper, but eventually do. At
worst, they'll eventually just tolerate each other; best scenario, they'll
become real buddies. The few who absolutely will not accept another cat will
generally start showing their displeasure by urinating inappropriately,
becoming very aggressive. There are advantages to adopting an older cat, but
truthfullly I've had more luck integrating kittens. There is less territorial
stuff, and kittens just have a way of rolling over on their backs and saying
"Don't kill me, look how cute I am" and I swear the older cat responds to that.
This hinges a lot also on how active and playful your cat still is. A kitten
can really make an older cat more active, almost like they go through a second
kittenhood (once they've accepted each other of course.) But most importantly,
it only works if the introductions are right and very slow. But I'm sure you
already know all about that. Best of luck. I say go for it.

Sherry