Joomla would also slow down our website and I never like the way it's structured. I enjoy working with more straightforward CMS such as Drupal, Typo3 or WordPress. We encountered this list of cloudbased CMS: http://www.cmscritic.com/dir/cloud/

Has anyone experience with them? Squarespace is out of question as they don't allow to host an app on an external subdomain.