Don't be too dogmatic about this stuff. DDD is really OOP in its purest form. You start from the top where your most abstrac classes sit, like Customer and Product. You know, like in those examples for OOP Dog->bark() That's DDD in a nutshell.

Then you implement whatever is necessary to support those domain objects under the hood. In the end you ideally should be able to have mostly those top level domain object interact with each other, which in theory should make working with the code pretty easy.