I work for a headless CMS, but I think that's a poor fit for your use case. Many of our small customers start off in your situation, where a helpful dev makes them a headless site. A couple years later, the dev moves on, and the client has no way to update their site with new features or sections, and no way to fix it if anything breaks. And we have to explain to them what headless is and why they're in this situation. It sucks for everyone involved.

Go with a regular CMS, like Wix or Squarespace or WordPress. The $10 or $20 a month is still cheaper than having to pay a dev later to fix their broken headless site with old deprecated packages and frameworks that nobody uses anymore.

Headless is a developer optimization, not a client feature. It only makes sense if the dev is a part of the customer's own team, or in an ongoing agency relationship with them. It's a poor fit for freelancers and volunteers because the client ends up with essentially abandonware.