Would like to add more robust encryption - Let's Encrypt plug-in Available?

Would like to add more robust encryption & still use the free SSL cert. On my Wordpress site hosted here. Do you offer "Let's Encrypt" or similar plug-in?

I have installed the free cert but FireFox still reports the images as unencrypted.

I don't see Let's Encrypt in my C-Panel options.

Do you offer it or a similar option?

Thanks!