cannot add configurable product to cart in magento when forcing SSL

[amajor]

Hello to all.
I wanted to use an SSL certificate on my shop and switch to a secure https domain.
Whenever I activate this rewrite in the htaccess file, I lose some functions:

## enable rewrites

    Options +FollowSymLinks
    RewriteEngine on
    RewriteCond %{SERVER_PORT} !^443$
	RewriteRule (.*) https://%{HTTP_HOST}/$1 [L]

Afterward I can only add simple items to the cart but not any with configurable options.
Also a display section does not show images anymore.
Whenever I click the add to cart button, a message appears, indicating, the information will be transmitted via an insecure connection although the https seal is visible but the cart remains empty.
I know this is a common issue but I have searched for a solution for hours without success.
JavaScript not be working properly? Is htaccess configured correctly?
Your help and effort will be greatly appreciated. Thanks Alex

[amajor · Accepted solution]

Solved.
I found the solution in a german post by Sebastian Keutmeier from www.maxanoo.com . Credits to you Sebastian.
He said: The way solve problems with switching to HTTPS is to keep SSL always on. This is a typical and recommendable way.
Go to system/configuration/web/secure
and add your secure https://yourdomain.com/ as base URL
Then copy the content from all fields from the secure tab to the Unsecure tab. So your unsecure base URL will also be https://...  and subesquent fields: Base Link URL {{secure_base_url}} and so on. Clear cache.

This worked for me.