Choosing a compatible 2nd dog?

My husband and I have a 12 year old male golden mix. His female companion passed away a year ago. Our youngest just went away to college and we work full time. He's been very lonely. Vet says despite some hip problems he's in remarkable shape. He's got some time left and we don't want him to spend it lonely. He loves other dogs and needs a friend. And though this sounds really selfish, we need another dog to help us emotionally when his time comes. I also like having a big dog around for security.

We found a 9 year old female lab mix that we really like. The woman she belonged to died in a car accident about a year ago, that's all we know about her past. She's a bit shy but once she decided we were okay she was extremely loving. She came to our house for a "home visit". Our dog got way too excited and happy. He was all over her sniffing and licking. She got pretty defensive. Not aggressive per se, she let him take the toys, but she's definitely not shy about saying "get your nose out of my backside or else". Showing her teeth and acting like she was gonna bite him. After about an hour he calmed down and she did too. Though she didn't show much interest in him.

My husband and I both fell in love with her, but we're concerned as to weather or not she and our dog would be friends. She currently lives in a foster home with 3 other dogs and from what we are told they all get along fine. Our lonely boy just needs someone to curl up with while we're at work.

I take him to my brother's house pretty often where they have a female collie/husky mix. They get along okay, but it's kind of the same thing. She growls and even snaps at him when he sniffs her. Is that fairly typical behavior? Our other dog wasn't like that, but they grew up together. Is this to be expected bringing a new dog in to the home? Not sure what to do.

Grateful for any thought or ideas on our situation.