I really like Kirby. Very customizable without the bulk code WordPress produces which I find incredibly frustrating and annoying. It does require knowledge of some basic PHP. A little more advanced than WordPress but nothing crazy. The only dislike I have about Kirby is the lack of a commenting system. You would either have to create your own or use something like Disqus. In your case, I think this would be perfect as it also has a backend service for your client.