Mixes! First find the smaller dog breed you like, then go on petfinder and find a mix. Or for PB, too, Petfinder. That way you can find a dog your dog really clicks with. It's fun to watch when that happens with two dogs.
I had Bella and Kramer, brought Bruno in (Schipperke-Shepherd mix, like mix perfection other than the barking and do wish he'd gotten a little more of the GSD biddability
) and they were like OMG!
THERE HE IS! Like they'd been waiting for him. He was about 6 months old.
Schipperkes really are great but can be a little pushy with large dogs, particularly the males, and are not great off lead for the most part. Bruno's first time off leash he ended up in a corn field which I had thought was no where near where we were at the time, but...he took off for that instead of running in the giant field we were in.
I love poodles (but not their fur-kind of weird to me). I think with the right GSD a poodle is an outstanding combo. Bella loves them too. She was fostered with one and when she sees one, gets very happy. The poodles and Bella would always play after obedience, and honestly out of the large class the bunch of them were absolutely the smartest and most well behaved in combination.
I like Spitzy/northern/ancient type breeds, but there is some mind of their own thing happening with them. Ava is a BC-Chow mix (I think) and man! Creepy primate intelligence mixed with deviousness...she is great.
A GSD is so different, I think, from other breeds, in a good way. But another breed can spice things up or calm things down, depending on what you like.
Going to a shelter or rescue you will have so many choices and your Ruby and you together will be able to make the decision. It will be great. Good luck!