Considering adding a small mouser

[Chicagocanine]

IMO you have to have the right home for a Jack Russell, they can be hard to live with if they don't mesh well with you, or if for example you are bothered by barking, or very high energy dogs, or dogs that want to play 24 hours a day, etc... Rat Terriers are slightly less lower on the "crazy terrier" scale than JRTs, and Border Terriers are probably a few notches down but still very good working dogs, they are often involved in Go-to-ground.
I had a Rat Terrier mix but he was a pretty crazy/hyper dog, kept me on my toes but I loved it and he made me really appreciate terriers, I'd definitely like to have another terrier in the future.

[pets4life]

be careful if it pisses your gsd off too much the gsd will kill it ive seen it happen, in a few seconds, ive also seen a gsd cause perm damage to a JRT in a split second by ripping open its anus during play. JRT like to be top dog but it wont last with a gsd.

[wolfy dog]

I will never have a JR, don't worry. Cannot do that to myself or to WD. I prefer dogs with an off button as well. Cairn or any small mix that will do the job and fits in a Sherpa bag for traveling with me will be eligible.

[Carriesue]

I have a Chihuahua mix, I 'think' she is mixed with Rat terrier but definitely some sort of terrier. She has never killed anything because there's nothing around here for her to hunt but she is vicious with toys and has crazy toy drive.

I have no doubt if presented with the opportunity she would though and oddly enough you'd think she'd be super yappy but she is SILENT. She never barks. She's about 18lbs too so not super Chi tiny. So I think what you're saying with a terrier or mix would be a great idea!

Pic of her

Sophie by Carriesue82, on Flickr