SFTP / Wordpress Permissions

It seems this question has come up quite a bit before, but I wasn’t able to find a working solution.

Installation: Ubuntu WordPress on 14.04

The problem I originally had was when I tried to upload a plugin for my Wordpress site through SFTP (FileZilla) using [userName] I received an error saying Permission Denied. I followed the responses from similar questions and did as suggested

sudo usermod -a -G www-data [userName]
sudo chmod -R g+w /var/www/

And was then able to upload files. However, when I went on to Wordpress and tried to update the new plugin, I was met there with a Permission Denied.

If I view the plugin folder within FileZilla I can see the Owner/Group is “[userName] [userName]” as opposed to www-data www-data as with everything else. I saw comments on other questions providing manual steps one could take to change permissions for the specific file, but I was wondering if there was a permanent solution as logging into the console and manually changing permissions every time could become tedious.