Please also note that "rescue" does not automatically mean "crossbreed". There are breed-specific rescues for almost every breed you can think of.
My only concern is that you work long hours and you don't have a lot of secure yard, so many rescues may not consider you as a suitable home for their dogs. If this is so, please don't take it to heart - they have invested a lot of time and energy into this dog who most likely has not had the best start in life, and they want to make sure everyone is happy.
Another option to consider is to contact registered breeders - sometimes they have older dogs available - either at the end of their breeding career and looking for a good retirement home, or a puppy they kept on as a potential show dog that didn't make the grade - nothing major, just some sort of conformation fault that only a show judge would see.
It may also be an idea to take your family along to a dog show, talk to breeders there, and also get a gauge on what dogs your son will like and what ones he will not.
To be honest, I think a puppy would not be suitable for your situation, but that is my personal opinion.
All the best with your search!