I would stay away from a Jack Russell. They shed terribly and can be quite the barkers. They're wonderful little dogs and insanely intelligent, but not fitting for what you have described (or seem to need).
As for breeder vs shelter, it's a crap shoot either way. I, personally, don't support breeders. There are far too many dogs that die needlessly everyday. That being said, the choice is yours
Now, for the purebreds! Just to give you an idea, my baby came from a breeder (we did not purchase him from the breeder ourselves, we obtained him from a couple who did) and we have spent over $35,000 in vet bills... and he's only 2.5 yrs old. That's not to say that all purebreds have issues, but many do, and due mainly to irresponsible breeding and over-breeding.
Shelters: You would be amazed at the amount of purebreds in shelters. You would have to check with your local shelter if you're looking for a specific breed, but another great option is a rescue. Many rescues have purebreds and there are also breed-specific rescues. Those are wonderful places to start in your search.
One thing you need to be aware of is that any
dog can have medical issues. Mutts, purebreds (even from responsible breeders)... they can all develop problems. You have to take that into consideration when getting a dog. You many not want a dog with health issues, but that may just be what you end up with. When you do decide on a dog, google it for known health issues. The northern breeds, like the Alaskan Klee Kai, are prone to immune-mediated issues like Hypothyroidism (Epilepsy typically goes hand in hand with the Hypothyroidism, but not always). Klee Kai's also, for reasons unknown, seem to develop liver and kidney diseases. I wanted one for quite some time, they're just adorable! But after having Malamutes, and the issues with both that I've had, I probably won't get another. They are also very prone to cancer. And being that the Klee Kai shares the genes, I would imagine they may be as well? Whatever you decide on, just do your research (which it seems like you are doing!), and keep in mind that any dog, at any time, can develop health issues that require large vet bills. Get pet insurance! Trupanion is a great one to go with. Here in Canada, they are less expensive and cover more than the ones my husband and I researched. They are also, as far as I know, the only ones to cover congential issues and have no lifetime maximum limit. Our sweet Nookie had his first seizure at 2.5 months old. We were in the process of getting insurance when it happened, so we were out of luck and have had to pay for all his expenses. Our shelter puppy has insurance and with all the issues that seem to be "the norm" these days, I would not have another without having insurance
Oh, one more thing... if you do decide on a Klee Kai, stay away from the reds! Red in any breed is a recessed gene, but in breeds where it isn't a common color and is specifically bred for, it can cause issues like the ones our Nookie has. Thanks to our wonderful vet (she wrote a paper on the "Red" gene and issues it causes), we will avoid them, as beautiful as they are