I have posted this on another thread about multiple cat adoptions on this site:
We have had multiple cats for the past 30 years and every time I have introduced a new member to the household, I will put the newbie in a separate room for 7-10 days to get the other cats used to the "intruder". Give it its own litterbox, bed etc in that room. Cats are naturally territorial and seldom will accept a new cat right of the bat unless they are very young kittens. Your cat is still young so I would make sure to get a kitten around 4-6 months old. Since you have a tom cat, I would get a female kitten. Opposite sexes tend to get along better. Make sure they are both neutered though! Go to an adoptive place that fosters cats in homes since the cats will be better socialized. You can also see which cat will be shy, friendly, good with other cats etc in that environment. After separating the cats for 2-3 days, put your original kitty up in your bedroom with its litterbox and let your new cat out of its confinement to roam through the house. Always supervise. Then put the newbie back in its room and let your cat out to roam. You are trying to get them used to their scents. After 6-7 days you can try to introduce them to each other while supervising. This requires some work but we have never had issues with cats hating each other when introducing them this way. Some have become best buds, some have gotten along without getting too cozy. The younger they were, the better they adapted. They tend to want their own food bowls but should be fine with one water dish (I have a fountain). Good luck 
I have three cats at the moment, all introduced at separate times and all rescues. My 4 year old female and 5 year old male (introduced to each other at 5 weeks and 1 year respectively) are the best of friends. My 12 year old female tolerated them both but gets along better with the other female in the sense that they actually cuddle up at times. Oh, I have two litter boxes for the three cats but have also had two litter boxes for two cats. Good luck