Getting a 2nd dog is a big decision. But, I do think 2 dogs keep each other company, give exercise and play to each other in a way we humans can't. BUT, the real questions are more about you and whether you are ready to take on 2 (or more...) dogs. [I say "or more" because once you have two, you'll start thinking about a 3rd...]
1. Do you have the space, time, and patience to devote to a 2nd dog? The two dogs will have different personalities, different learning curves, different misbehaviors, etc. Just like kids, they will be DIFFERENT dogs and will have to be managed / interacted with differently.
2.Are you ready for the added complexity and expense this will entail? Double the expense of vet bills, medication, food, grooming, beds, toys... You need a car you can easily transport 2 dogs in. It will be harder to find pet sitters or house sitters. Harder to find two spaces in a kennel if you have to board them.
3. Are you actively giving your current dog enough exercise and stimulation every day? Sure, the 2nd dog will provide companionship, play, and exercise for the first dog, but it's not like you can just leave them on their own. You will be exercising, walking, training, and managing two dogs at all times.
4. Being out in public with 2 dogs (walks, going to Starbucks, darting into Home Depot... or just dealing with other dogs & owners you encounter) is not just 2X harder with 2 dogs, it's more like 4X harder. You have to really know/trust your dogs -- and they really have to know/trust you. You really have to commit to training and teaching them if you have 2 dogs. With one dog you can sorta fake it. Can't fake it with 2.
With all those warnings, I still say: considering it strongly, but realize how much of a responsibility it will be. I will also say: consider getting a 2nd GSD. Their temperaments, training, intelligence, exercise needs, size, etc. will match.
We currently have two GSD's (a male and a female). They've been together for 5 years now. After having 2, I can't imagine how, in the past, we only had one GSD.
One other piece of advice: Figure out a situation where you can have your current dog meet the (prospective) new dog -- on neutral ground -- before you make a decision on the 2nd dog. We did this and were able to see that our 2 got along from the first moment. Do not bring a new dog into the house without assessing compatibility first.