REALLY SIMPLE SSL PRO

Really Simple SSL pro Features
Extensive scan which enables you to detect the source of mixed content that couldn’t be fixed automatically, with fix button
Premium email support
HttpOnly and secure flags to make the cookies more secure
Improve security by enabling HTTP Strict Transport Security for your site
Submit your site to the HSTS preload list
Warning by email and in your SSL dashboard when your certificate is about to expire
Mixed content fixer for the back-end
Note: You have to install and activate its free version in prior to using this plugn. Download it on Wordpress.org here.