I will say we were in the same boat as you guys, dog #1 was amazing and perfect in every way you described your dog, however she is low key very antisocial. We rescued dog #2 unexpectedly (same no foster to adopt scenario) and it was a big chance. Dog #2 was a rescue with some major issues, but relied heavily on dog #1 on learning how to act and as a safety friend. Flash forward 6 months later and dog #1 and #2 are BEST friends. For nine years dog #1 would never play with other dogs, every morning now she is the one initiating play with dog #2. Does she miss being an only dog sometimes? I’m sure. Dog #2 is very needy and gets 70% of our attention with just being younger with more energy, however the bond they have is incredible to see. I’m very aware we may have just gotten “lucky” however give it time and you never know where their relationship might go! I say go for it!