I have similar issue on one of my domains. I have SSL cert installed both for naked and www-domain.
Now, however I want to redirect both naked http://domain.com and https://domain.com to https://www.domain.com.
I have this rules in my .htaccess, but it covers redirect when you visit site explicitly with https://domain.com, but, when visiting http://domain.com, it redirects to http://www.domain.com instead https://www.domain.com.
RewriteCond %{HTTP_HOST} ^[^.]+\.[^.]+$
RewriteCond %{HTTPS}s ^on(s)|
RewriteRule ^ http%1://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]