HubSpot requires using CNAME to point a domain to their server using a subdomain. This means you still have an A record to worry about. The www in your www.yourdomain.com is a subdomain and not root domain that does not have the www. It is the same as blog.yourdomain.com or mail.yourdomain.com.
In order to fix this, you need to have an SSL certificate on the server that your root domain is pointed to. This is most likely your domain registrar like Godaddy or namecheap. These do not have secure domain forwarding and so you would need to purchase hosting, SSL certificate, and do a server side redirect to your HubSpot site using www. Are you lost, I know this can be confusing.
HubSpot has this support article that provides some good solutions to easily fix this issue.
You can consider the following options:
- Use a third-party service, such as EasyRedir, that provides this functionality. EasyRedir also has a support team to help along the way.
- Use a DNS provider that supports this functionality. It is recommended to contact the potential DNS provider directly prior to purchasing their services to ensure that they can provide the functionality.
- Purchase a server, install an SSL certificate on that server, and configure that server to forward traffic from the secure apex domain. (recommended solution)