The only thing to consider in this case is how you have configured your site. Browse for a while your site and see if the address stays with or without www in front.

If the address stays with www, then your site has been configured to work with www and your SSL has to be ordered with www. On the other hand, if the address stays without www then you should order the SSL without www.

Alternatively, if you are a SiteGround customer, you can order a Standard Alpha SSL certificate which will work with both yourdomain.com and www.yourdomain.com.