Module Smart Menu for Joomla is free for download. Smart Menu will show ONLY first level menu. NOT sub menu. Only for joomla 3.x

Smart Fixed Navigation

"A fixed navigation that allows your users to access the menu at any time while they are experiencing your website. It's smaller than a full-width fixed header, and replaces the back-to-top button with a smarter UX solution.
 
Web pages with a lot of content require a quick way for the user to get back to the top, where the navigation is (most of the time). Hence the old back-to-top button. But why should the user scroll back to the top, if we can make the navigation accessible at any time right where the back-to-top button is supposed to be? No reason in 90% of the cases. For the remaining 10% we are still covered, since we created both a fixed headernugget and the back-to-top snippet ;) " - from codyhouse.co
Check demo: