Nobby presents tartan design harnesses to match with collars or leashes for minis and small dogs.

If You are stuck on choosing between a harness or a collar, I can only point out that you can guide the dog with more energy without doing any harm to his neck. At the same time, there's a tendency to heavily drag the dog with the harness, which is not good either. To avoid that, it would be the best to teach the dog to walk beside you.