How to change the site URL to use WWW

Ok, so I’ve installed example.com as the root site for a multi-site network, example.com has one page that needs an SSL displayed on it. The SSL was not displaying properly and I found out it’s because the certificate was set up to use http://www.example.com and so it’s reading it as unsecure. I have tried everything I know to change multi-site to use www. I got into the database and manually changed siteURL and homeURL, I updated the wpconfig.php (which leaves it redirecting to the home page no matter what you click on). It’s very confusing. I’ve read several places where people say not to use www, but no one says why… I’m using folders not subdomains because of how this particular site needs to be set up (which is why I’m guessing normally www is a problem). Any ideas? I’m at a loss and don’t want to have to pay for another SSL Certificate…