I have flagged this issue in the past - and there has been a flurry of activity on the Atlassian side after so many users complained at not being able to edit full width on pages using the new editor.
But I simply can't find a way to open up a single column section using the editor. when you select the 'Layouts' menu item It offers Two equal columns, two unequal columns, three columns or the Bin. Nothing else.
So my question is still... how do you ADD a single column section - which is what 99% of our content has today? Am I being thick here, because it was in the old editor (which we still use because of this issue)?