Have you considered a non-working line cocker spaniel? If you like your current dog but want a calmer version? Or a King Charles Cavalier, which are quite similar but were bred more as companion animals. Both would need to have considerable amounts of health testing done, but if you are serious about it could make great family pets.

Another breed you might consider is a whippet. Again, health testing is a must, and you may need to make some adjustments to your lifestyle for the colder months. Some can be prone to anxiety, but many are quite stable/independent.

I am a high drive, high energy breeds person myself, so I can't speak from a great deal of experience with calmer breeds other than passing interactions.

 

Female Rough and Smooth collies would fall into your size range when bred to the British/European standards. They are usually friendly (although not overly loving) towards other dogs and people, and they are fairly easy to train. Mine had very low interest towards prey animals (but I've also met collies who like to chase hares) but she liked to play ball with me. The breed can be sensitive but it is from the less demanding end of herding breeds. You have to screen the breeder carefully to avoid nervousness and fearfulness. I'll admit I'm somewhat worried about the breed's genetic diversity.

Whippet also occurred to me. I don't know how common nervousness is in them as they look a bit timid but it could just be that look of theirs. Sighthounds can have prey drive but is it uncontrollable? I've also heard that whippets and greyhounds can be lazy at home but really enjoy if they have a good run off-leash regularly.

Do you know anything about companion spitzes like the Keeshond or Eurasier? German spitzes have also smaller varieties. These breeds were bred to be living doorbells so they can be barky.

I don't have experience about dogs with kids but a stable well-trained dog should be fine with your kids.

 

While different breeds are certainly known for different traits, I think a lot of your concerns will boil down to the personality of an individual dog. I would definitely work with a small preservation breeder that knows her bloodlines and can tell you how the temperaments run.

I also think much of your future household harmony will depend on your new pup's ability to get along with your current dog. If your girl has a health issues serious enough to affect her ability to exercise, I expect some amount of pain is a constant background sensation for her. Pain will make any creature irritable. I expect your new dog will need to deal with some grumpy cocker snarking. Your new dog will need to be able to shrug it off instead of snarking back. Therefore, in your shoes, I would consider an even keeled temperament and good dog sociability to be the most important characteristic. I would even sacrifice trainability to get that temperament.

As far as breeds, I would look into breeds that were bred to work in close proximity to other dogs when all the dogs are highly stimulated. That tends to be hunting dogs. Hunters don't want their dogs going over threshold and snarking at another dog out in the field. Beagle would be top on my list due to their size, their sociability, and their sweet temper. They aren't as trainable as a herding dog or a retriever, but they make up for it with a general tendency to get along well with other dogs and children. Bench Labradors and Golden Retrievers would be second on my list, but there will be a period during adolescence when they don't know their size and will have a tendency to flatten their playmates. Also, badly bred Goldens and Labs never grow out of their puppy exuberance. I've known quite a few badly bred retrievers that are still bouncing around like pinballs at age 7 or 8.

 

The main consideration is your current dog. Is your current dog approprate for adding a 2nd dog? Will your current dog help with a new dog or will they interfer. A dog that is dealing with health issue is a dog that can over compensate behavioral wise, defensive because they don't feel well or in pain and feel more vounerable to be defensive. It's a big consideration for me because you could could ruin the good dogs ,you have and the comfortable time and effort working with your current dog that needs your time) youfe have and also ruin the new dog you bring in. You only have one slot for a second dog, and you only have only so much time in a day, and so much living space) you may still have these 2 dogs if you bring a baby into your house hold in 5 years. A new dog will not change your current dogs situation it could exagerate it.. And if your feeling challenge with the current dog, consider loosing the joy of a 2nd dog when it creates more problems more time, more stress and you end up with a second dog that has behavioral problems for their life time.

It's not worth adding a 2nd dog when the first dog needs special consideration. I say wait on a second dog especially exposing a new puppy to the experience. Enjoy your current dog as they age out. Maybe in a few years your current dog having your undivided support will be more appropriate a good mentor in bringing in a puppy. It wont matter what breed of puppy you bring in, no matter how well bred that new puppy is. your experience is based on your current dog.

When my senior female corso passed away, I did consider filling that working dog slot on my farm. It was such a thin thin line of my Corso and female LGD getting along for a life time. I just wanted to enjoy the extra space and enjoy my senior female LGD for the short remaining years she had left. Im glad I waitted. Give it some good thought.

In the future looking for that right pup. Find a breeder who has an active puppy start program and consider allowing the pup to be older in a breeders enviroment that knows how and is set up to do all the basic foundation exposure. Getting a puppy at 4 months old that has stay'd with their litter mates learn to play in a group and interact, their dam, been around appropriate adults dogs, maybe even exposed to appropriate cats. Been put on a daily routine,potty trained, handled by humans. A starting foundation for you to build on. It's a myth that a puppy wont bond if you get them older is false, they will search for the positive relationship that their breeder started and nurtured in them.