Choose an SSL certificate
Start with the addresses that need HTTPS.
List your website names
Include the main domain, www and subdomains. Check which names the certificate covers; a wildcard does not cover arbitrary subdomain depths.
Validation and maintenance
Check domain validation, hosting compatibility and renewal. Let’s Encrypt describes HTTP-01 and DNS-01; its wildcard certificates require DNS-01.
What HTTPS provides
A certificate protects connections, not application vulnerabilities. See Besthosting SSL certificates or installation guidance. A Bestname domain certificate is a different document.