Hi, my old GSD used to have this problem and as we‘re tiled throughout, we did more or less the same as Jaysmumagain. The food bowls used to stand on large a rubber backed door mat so that the dog, and the bowls, had a good grip. I‘ve not heard of the paw soother, in my dog‘s case I think it was more down to weakness in joints and hips. You might possibly try raising the bowls? If the head is raised, it might help the balance? - just a thought....
Hope you can find a solution, its painful watching them start to struggle, I do sympathise....