I haven't had back acne since I started using Dr. Bronner's Tea Tree. It has a tea tree scent, so it isn't exactly a pleasant fragrance, but it's not a bad one either. I like that it's an all-in-one product that can be used from face to body. They say it's gentle enough for babies to use.
I bought the large size for around 18,000 won on sale, but it's a bit inconvenient because there's no pump.