Welcome to PT!
Adding a second dog (or any pet) does require some serious thought. Like you said sometimes it could be the best decision made, sometimes the worst.

You say your dog likes other dogs, that is about the best start you can have. But there are other factors that you have to consider.

Fist of all can YOU afford/handle it? You'll now have to spend twice as much money & time.

Although your dog likes other dogs, does he get jealous easily?

Are you prepared & can you handle keeping them seperated at first if needed, until they adjust to each other?

Has he always been an only dog? Have you ever had other dogs in your home or on your property? If so how does he handle it?

Do you have any idea what breed &/or age of dog you would like to add to your family?
A younger puppy or one that has been around other dogs would be best. A shelter or rescue organization should be able to help you make your decision and will allow your dog to meet the future dog to see if they get along. Some will even allow to foster the dog or even allow you a trial period. If things don't work out they will take the dog back.

Should you decide to get a new dog you want to make sure your previous dog still has "his" time and make sure (at first anyways) your dog comes first so he knows he's still loved.