I think the Scroll to Top extension is excellent/useful and will satisfy your needs.
https://addons.opera.com/en/extensions/details/scroll-to-top/?display=en
It gives you a scroll arrow on the bottom right hand side of the page (good for multiple pages) especially good for scrolling down and up. You can scroll all the way up (when you're at the end of a long multiple page article) with one click of an arrow, or a page at a time up (if you're trying to find something you read that occurred earlier).
By keyboard, you probably know Ctrl-End takes you to the bottom of a page and Ctrt-Home takes you to the top.