Hello, I foster dogs for rescues so have had a wide range of breeds. This might sound negative but I hope it's realistic
As you've said you clearly don't have time for a puppy. The toilet training etc will take a lot of time and energy. I would recommend that you look at the puppy threads on the doghouse section of mums net. Also i would be concerned about mouthing and Nipping. Pretty much all younger (under 12 months) dogs will go through a stage of mouthing and nipping. Depending on the dog, depends how long this lasts. Anything with a Labrador etc in it expect lots of mouth related behaviour. I would be concerned that once a dog nipped your son in play, your son might develop a strong fear reaction and be unable to tolerate the dog
Each breed matures differently but I would expect a lab for example to be in the naughty adolescent period until around two. This might mean stealing things, being really bouncy and generally a teenager. Would your DC tolerate a young dog stealing a toy that's laying around or being pushed out the way?
I'd not recommend shepherd breeds for the tendency to herd and as a result nip. Anything high energy that doesn't get an outlet for this is likely to become an issue. Take border collies and some spanials etc, crazy intelligent but can be bored stiff by domestic life. Dogs like that are built to work on a farm or chase things all day without becoming tired, that means they may be overwhelming in a home environment.
Romanian dogs etc often come without a history. The rescues homing them tend to be less strict around rules about being left or childrens ages etc so lots of people chose them. However they are often a complete unknown. A dog that is found on the street has a whole history of scary things that no one knows. If it's never been around children, in a house, or a pet then it's likely to take a long time to settle. For example we had one that barked non stop at photos because he has no concept of what they are, he is very traumatised by his past and despite being exceptionally behaved now he has quirks such as hating football's that must stem from way back when. I'm also sceptical when a street dog who had never been in a house before is rehomed by a rescue as being good with kids etc.
What is recommend is figuring out what are your deal breakers. E.g. could your son tolerate barking? Can you tolerate having long walks whilst dc is at school? What kind of play are you looking for?
Ultimately it will be your dog and what happens if son doesn't like dog or if dog doesn't like son (I don't know what home is like but a child that's noisy, unpredictable, plays too rough or volatile might mean the dog doesn't like them or in a beat case scenario is simply not interested.)
There's lots to think about and I hope that you find something that the right fit :)