I would almost go as far as saying he is lazier than my cats! He loves to snooze and cuddle up on the sofa but also loves coming to the yard and going for walks. He is a fantastic dog - friendly, lively and fun but also snuggly and sleepy - everyone loves him! He has 2 walks a day, just 10 mins on lead in the morning, and about 40 mins off lead running around fields in the evening, plus long walks at weekends, and probably spends another 2 hours every day messing around at the yard. He does like to protect his home in his own little way so will bark at cats in the garden or noises outside the front door, and he has been very very well socialised with other dogs - I think this is really important for JRTs.
I think my younger girl would get on well with any breed but I'm not sure about the older girl who is very fixed in her ways?
Clever, loyal, affectionate and fun. Mine is 4 now and my son has one as well who stays with us a lot she is also 4. They are great. My little one comes to the yard and helps me round up the chickens when they are "free ranging" she knows not to hurt them. She does steal eggs though
She runs and digs and ferrets around while you are out with her but sleeps like a cat indoors. She is a lap dog at night. My sons is the same. They are both very very good with the small children in the family and tolerate quite a lot of tugging, pulling, carrying and teasing from other peoples children. They are, however, terrible scroungers and thieves. In case you cannot tell I think they are the ideal family pet - mine is also good with cats, other dogs and horses.
You'd have to work on introducing a puppy what ever breed you chose - but it's got to be a Russell!!
If she was allowed, she'd be up on the sofa for snuggles all the time, follows me wherever I go, but in no way needy and happy to wander off and do her own thing. Never been in any way snappy with kids or anyone (which some JRTS can be) and if someone will give her a belly rub, that's it, firm friends! She also takes herself off hunting overnight sometimes if we haven't closed her up early enough...
Will have to wait a while to get one though because we are having more building work done over the next few months and it would be a bit hard to keep a puppy in if builders have removed the front doors 
He came with me everywhere, never on a lead, and kept up with a pack of kids on bikes all day. 
) is a vicious little ******** of a dog, has bitten dogs and humans alike and is nowhere near as receptive to training. It is almost entirely their fault for being numpties but even as a pup there were striking differences in his attitude compared to the previous one.
i dont know if its due to the fact mine is the runt and we think she isnt a jack russell.. looks more like a chiwawa.. (sp!!) .. she can be moody.. she is lovely to us and to have around.. but we can never trust her with little poeple.. as i said.. this may be due to the fact she is a bit "special" .. however she did enjoy a 8 mile bike ride the other day and caught her first rat! ..
xx