lilybull on "Adding an SSL certificate"

I was wondering if there is an SSL certificate I can purchase for my website. It is currently set to private but when it goes live readers will be submitting information. Therefore if I believe correctly it is law that my site be secure from hackers, etc. who can access their information. How secure are wordpress sites and can anyone recommend where to buy an SSL certificate and how to add it to my site.
Thanks any help would be appreciated :)