Low energy/relaxed dog breeds

So we have a 7, almost 8, year old rescue dog that is mostly Jack Russel but has some other breeds mixed in. He’s the complete opposite of a Jack Russel in that he is a napper and low energy, walks are done but he isn’t a long walker and will not do hikes for long. A few runs around the fenced area, a few ball tosses, and he just wants to plank on the deck and relax. Good with our young kids (under 6) and really we know we got lucky with him.

Any ideas on a breed that will not destroy this nature of him. He’s very well socialized, numerous family dogs and frequent visitors so not concerned of adding but can’t decide a breed. He’s 18lbs so my dreams of a Scottish deerhound aren’t going to work.