Professional dog trainer here:
I would highly recommend contacting local rescue groups and giving them your scenario and wish list. "We can commit to x hours of exercise per day, looking for a dog that is good with kids and between 20-40 lbs, no excessive drooling please" or whatever it may be.
A good rescue will work with you to find the right fit. They will help you make a decent choice, and since most groups in the area have their dogs in foster homes, they have a more accurate view of what the dog is going to be like in a house. Sometimes with shelter dogs their personalities are really shut down (or hyped up) in a stressful shelter environment.
I would look at a dog 3+ years. That is past the puppy crazies, and their personality is more set. You will know what you are getting. Puppies pee, chew, run into things, nip, etc. It can all be trained and quelled, but it's a LOT of work if you don't know what you're doing. You will absolutely still need to train an adult dog, but it will be physically/mentally capable of the training, having outgrown its puppy brain
I'd go on petfinder and look for rescue groups in your area. Many do adoption events at the local pet stores, and you could go talk to a volunteer and get a feel for how they can help you.