Heh, that's pretty similar to my website layout.
The only special thing I had to do to make it work on phones is add a breakpoint for the menu across the top, so below a certain viewport width it switches to a collapsible dropdown menu. Feel free to steal my CSS if it looks like what you're trying for! (Only the front page has a sidebar, the rest are one column layout.)
Oh the other thing is, don't specify width for the main body, specify max-width. That way it can shrink on smaller screens.
HTML almost has to be forced into non-responsive layouts - but that's been so normalized that people forget that it's easier to just... not do that? And let the text flow according to screen size?