@Misadventure Check to see, perhaps, if there are any local shelters with slightly older (not ancient, just not necessarily kittens) litter-trained cats they want to adopt out in pairs.
No, really. Even cats 1-2 years old are still very young for cats, but hard to adopt out, especially in pairs.
Not only will the shelter love you, but they are past the 'kitten hyper' stage, and may not harry the older kitty as much. They also have their personalities already, and you'll have a better idea if they'll mesh well with your current kitty.
I've done this twice (two pairs over the years), and never regretted it. The two kitties I have now are actually sisters, adopted like this. Old pic but relevant cuteness:
...they are giant derpybutts and we them.
...and generally on-thread, we lost our Ancient Cat last year, in the midst of The Year From Hell.
This was Ancient Cat:
She was our puffy little snarkbomb grumpybutt. We called her my 'Overly Familiar'. That my overly familiar was a little ball of snarkitude with creepily human expressions should surprise exactly no one. We still miss her wee whiny face. (Sadly, all the pics of her being equally adorable are actual film and therefore are not handy, meh.)