[liketheketchup]

If you have mostly static web sites with little work to update, you could try out the flat-file KirbyCMS: https://getkirby.com/ - it is a CMS I tried myself and liked quite much.

I want to point out that it is not an open-source project like Wordpress, but a one-time licence fee you have to pay once you go live with your project.

There is a great community around KirbyCMS who are building plugins for it, for example the SEO tool you want, in this case it is free / "pay what you want" pricing model, so it should be quite affordable: https://plugins.getkirby.com/tobimori/seo

edit: also this could be of interest, as it has the intention of helping to do SEO checks when migrating from WordPress to Kirby - https://plugins.getkirby.com/johannschopplich/seo-audit