Installation failed: Could not create directory.

I have my server configured and setup on a VPS, running Ubuntu 16.04. When I first installed wordpress I couldn’t install any plugins at first, so I had permission setup like this:

sudo chown -R sammy:www-data /var/www/html
sudo find /var/www/html -type d -exec chmod g+s {} \;
sudo chmod g+w /var/www/html/wp-content
sudo chmod -R g+w /var/www/html/wp-content/themes
sudo chmod -R g+w /var/www/html/wp-content/plugins
sudo chown -R www-data /var/www/html

After I did all of this I was able to install plugins and continue with the work but I was not able to submit any form I create. I have used Contact form, visual form builder couldn’t be used to create a form. So after a while I tried to install another plugin and I got this error message again:
Installation failed: Could not create directory.
What can I do to permanently give write and execute right to webserver so things can work smoothly on the website.

Thanks