Just keep in mind that different breed characteristics are not guarantees of behavior patterns, but tendencies. Every dog is an individual: I had a very laid back, friendly(!!)dachshund for 14 years.
Hounds and working breeds tend to be a little bit more mellow, terriers more 'high strung'. We refer to ours as terrors, not terriers
: they're ten years old now and I've only seen the female close her eyes a couple of times...seriously.
Training and socializing makes a huge difference, too, so while you're researching breeds, don't overlook trainability.
By the way, the word Terrier comes from the French word for earth, or dirt, (terre), and they were bred to dig, usually after rats or weasels raiding grain stores or chicken coops, and every terrier owner I've met has confirmed that particular trait.
Good luck in your search.
Stephanie