I've been using FillColumnIndicator and it's exactly what I'm looking for except that the vertical bar at the text width extends only to the last line of text (doesn't extend across the entire buffer)--not a big deal. But I'm having issues making it toggled on by default when I start emacs on all modes (I'm a complete noob), despite adding the following into init.el:

;; turn on fci-mode automatically for all files
(add-hook 'after-change-major-mode-hook 'fci-mode)

;; enable fci-mode as a global minor mode
(define-globalized-minor-mode global-fci-mode fci-mode (lambda () (fci-mode 1)))
(global-fci-mode 1)

For example, when I startup emacs and enter the scratch buffer, it's not enabled and when I open the init.el file, its still not enabled. I haven't dealt with modes yet so haven't tried changing modes to see if it indeed does get enabled as the setting suggest, but in any case, the above settings don't seem to toggle the settings on by default (I would think the second setting where fci-mode is enabled as a "global minor mode" would be what I'm looking for but apparently not.