Nobody seems (apart from one comment) to have pointed out that Opera does exactly what is asked for. It saves the page as one selectable PDF Page without cutting adverts! nor add page breaks! and exactly[*] the current view width narrow or wide.
Here we are viewing Narrow Page 1 at the bottom so the PDF in the center is one long page and zoomed in on the right we can see width has been ALMOST[*] exactly used.
[*] The difference is the scroll bars are removed on saving so the width is slightly wider and collateral damage, in that case, there is a slight shift in contents.
Image may be NSFW.
Clik here to view.
[*] NOTE There are hide scrollbar extensions for chromium's like Opera but results can be variable. However, checking the "nominated site" and Hide Scrollbars it shows it can be activated.
