Mac CRM software with iCloud Contacts integration
I don't know much about the software, but it seems like Contacts Journal may do what you're looking for, with two caveats:


new contacts entered in Contacts.app are not automatically imported into Contacts Journal, but it will automatically prompt you to do so, and thereafter keep the contacts sync'd
contacts added directly in Contacts Journal will not automatically appear in Contacts.app, and I don't see an indication of how to accomplish this.


There is a lite version that you can try for free, and also a FAQ.

I have no affiliation with the product.