We are currently working on designing a Responsive Web Site for a very niche market. The user base (elderly) would be using this site purely from content consumption - reading perspective more than anything else. Homepage is having main topics (level 1). Within each topic, there are multiple categories (Level 2)(currently hundreds, growing towards thousands, having really long names) and under each category thousands of articles (level 3) are present. Each article may have the article outline/sections within it. (Level 4, dynamic menu)
Now, on mobile device, we are willing to go for hamburger menu and keeping it sticky. This will solve accessing purely level 1 menu. As level 2 & 3 comes with big number, we can not show it in hamburger. (who will see scroll to see 778 categories in off canvas hamburger menu?). Hence we think combination of navigation pattern should be used. Mostly within page sticky menus can be used so that it will not hamper reading activity and will keep menu accessible always to jump from one section to other. Is there any way we can still use hamburger menu? What type of navigation patterns should be used here? Any examples for such menu and content heavy sites in RWD?
We will be using and supporting Search but just don't want to fully rely on it. Please suggest.