To setup a self signed certificate, thus ensuring your domain name is isolated / separate simply follow the steps below.
1. Log in to your cPanel account
2. Select TLS / SSL Manager.
3. Click Generate, view, upload, or delete SSL certificates.
4. Under the Generate a New Certificate section, enter the domain name as www.DOMAINNAME (where DOMAINNAME is your domain)
5. Complete the shown fields, then click Generate SSL
6. Return to the TLS / SSL Manager then click Manage SSL sites.
7. Click Select Domain, selecting the domain name which needs its own SSL cert (Self Signed), then click auto-fill by domain
8. Finally, click Install Certificate.
Within a few minutes the site will then use its own self signed SSL certificate.