A long article asks for attention over many minutes. The page around it should not keep bidding for that attention. Quiet layout is a reading tool.
Give the text a single column
One column, a comfortable line length, and space between paragraphs let the eye move down the page without hunting for the next line. Sidebars full of unrelated links split that path in two.
Let headings do the navigating
A reader who wants to skip ahead should be able to use the headings, not a floating table of contents that covers the paragraph they are on. On a phone, anything stuck to the screen competes with the sentence underneath it.
Save the next step for the end
Related articles are useful after the piece is finished. Placed in the middle, they invite the reader to leave before the argument is done. Finish the article, then offer somewhere else to go.
Open one of your own long posts and notice where your eye leaves the text. Those are the spots to simplify.