New Sibling for Manx boy

I currently own a 1 yr old Manx boy. As of right now I am unable to get a 2nd cat, but I would eventually like to get a 2nd cat. My boy is very social and loves attention, I fear that when I'm out of the house he will get lonely. We currently live with my parents so somebody is always home, but when I move we will be on our own and I will be out of the house often. So I thought that he might benefit from having a buddy. That being said, I'm doing research on what would be a good cat breed to pair with him. I would LOVE to get another Manx but they are a tough breed to come by, so I'm considering other options. As well, I've been told that a Female would be better to pair with him then a male kitten.

Don't get too hung up with sex and breed. Genetics and environment play a role in a kitten's development and you can never know how an individual cat will be in a particular environment, each cat is unique.  

Buying a kitten can be problematic in that you will not know what it's like until it reaches adulthood. If you want to be perfectly sure about a cat's personality you could buy an cat who has been retired from breeding or an adult which has been surrendered so that you know it's background. 

I have two British Shorthairs who tend to like to not get on your lap or be held, yes, you can say that of BSHs but you can say that of most large cat breeds. And yes, they follow breed characteristics in that they are independent but apart from that their personalities differ radically. 

I agree that it depends on the indvidual personalities. I've always done two males but mine are neutered and that plays a factor in it. I'd go with a personality that compliments your cats when the time comes. It is true that opposites can get along wonderfully but a high energy cat is usually too much for a really mellow one so you do want to match energy levels.

I have two Manx cats. The female was first and soon followed with a male for the same reasons you mentioned. My mom liked mine so much she got a brother of my male ( different litter.) They are all totally different. My female is sweet loving, refined and independent. My male is laid back, super cuddly and huge. Mom's male is smaller than my male, very naughty and very funny. Mine get along well and play some, and bathe each other. But, when I visit my mom it takes them a few days to adjust then it's on for the boys. They play so much! It's like watching two michivious boys. I think it's size and personality. Manx cats are known for adjusting well to other animals. Mom's boy tries to play with my female and she swats him! Lol. She's not scared in the least, they don't fight, I think he just gets on her nerves. I really wish my male had him to play with full time.