First I would suggest to go for a rescue dog, my family had enjoyed rescue dogs for some generations and they have never disappointed us. There are a lot of dog in the shelter who have been trained and are waiting for a new home to love.
Puppy’s are very cute but need a lot of care and training in their first year. Even dogs go through a teen period, which is not always easy. And they have a lot, and i mean a lot, of energy.
I don’t know how you guys live, but If you have a garden, and not a lot of stairs you can go for a bigger breed. If you live smaller and maybe also higher with a lot of stairs, a more small breed will be great. However, this is a guideline; Ive got a niece with a 64 kg dog living on the 7th floor of an appartment building, the dog just casually takes the elevator everyday ;).
Bigger breeds that have the reputation of being easy and sweet are Golden Retrievers and Labs. Myself i love Spaniëls and Setters. They are very kind, soft and easy medium breed dogs. As for small dogs, terriërs have a lot of character and energy. Every mix breed is great when it comes to small breeds, but I would be carefull with Pugs, Cavelier King Charles Spaniels, French Buldogs and every other Fashion Dog breed. Those dogs are prone to having a lot of diseases and most of them have serious difficulty breathing :(.