If you want a 100% uptime website that can handle surge traffic but also costs basically nothing when it's not being used, you're going to want to avoid traditional CMSs like Wordpress and learn to code. Deploy 11ty to Netlify with the understanding that if you're irresponsible with forms or suddenly blow through your bandwidth you're going to pay for the service to scale to meet demand.
If you absolutely must have a CMS, I'd recommend Statamic because it can act as an SSG and deploy to Netlify (which means you use the CMS as a local devtool only - no logging in over the internet). It's another one of those "bring your own front end" CMSs, but their Antlers templating language is completely fine.