Many people in the comments recommended using WordPress, and for good reason. Your client can manage their content on their own, and WP will be around for the foreseeable future.
If you want to use WP as usual and get a headless output in one click that even your client can generate, check out Strattic: https://www.strattic.com (Disclosure: I'm from Strattic).
If you want to use WP as usual and get a headless output in one click that even your client can generate, check out Strattic: https://www.strattic.com (Disclosure: I'm from Strattic).