Very sorry to know you lost Harvey, and think that a companion for Ollie may give him a renewed lease of life.
Availability of kittens does seem to vary from area to area, but I agree that sometimes kittens that are out of those early stages of kittenhood can be just as easy to slot into a family as very young kittens, so might be worth asking about cats in the 4 - 6 month brackets too.
I dont think sex matters too much either (although on the whole I do thinks females are bossier than their male counterparts
)
With regard to introducing your new family member when the time comes, there's loads of good advice on the forum int hat regard and we'll all be happy to help the process along if you get stuck. We will also hector and badger you for photographs, so be prepared.
Do you have any photos to share of Ollie?