Ignore anyone who tells you your dog is skinny. Far too many people have become accepting of obesity in their pets. You see it all the time in vets and parks.
Our GS female weighs 27kgs. She is just pure muscle. Everyday she goes for a free-run or 1-2 hour walk as she has to be fit for shows. The amount of people that tell us she is too skinny is astounding. I think there is such a disconnect nowadays between what is a healthy weight for pets and
Your dog's weight looks fine to me. I personally like my dogs to be on the lean side. Obesity wreaks havoc on a dog's joints and it is so so important to keep the weight off older dogs especially.
Always go for a grain-free brand of food if you can. A lot of dogs are allergic to corn and I do not like to see it in any of my pet food. We are very limited in brands here in Australia (we feed Earthborn Holistics Primitive and Eaglepack Holistic), but the site http://www.dogfoodanalysis.com
has tons of info and reviews. Plus it explains what to look for and what to avoid.