Thinking of getting a second cat?

I'm getting ready to move out of my house and into my own apartment. I got my cat about 4 months ago, and he's got an excellent disposition. Very friendly and playful, affectionate towards people and (to an extent) other animals. Now, he's gotten used to me being gone for a good chunk of the day, and my dad being around for most of the time. He still sees me as his owner (when I'm home hes always with me, and doesn't spend a lot of time with my dad), and as long as I'm around he handles new things well. I'm just worried that he's going to be lonely while I'm out since I'll be living alone. I think having a buddy around the house would be good for him. I'm curious as to whether I should look into certain cats. Like how old should the new one be, what gender/breed, what disposition etc...

I have introduced my cat to my cousins cats and my girlfriends dog. He got on ok with the cats (they were much older and saw him as an intruder) and he handled my girlfriends lab fairly well until the dog spazzed and decided she wanted to give my cat lots of sniffs and kisses. Even then all my cat did was run to a safer spot and meow at the dog loudly. So I think he could handle a playmate.

Milo is a 1 1/2 year old DSH, male that's been neutered. Any advice welcome! Thanks!