E+ vs E- has no bearing on the width of the seats - they are just as narrow and uncomfortable - the only difference is a few extra inches of legroom. Most people find a 17" 737 seat with minimal padding generally OK for a 3-5 hour flight, but not for 9+ hours.

If one finds a very cheap international fare, but won't or cannot upgrade, it's quite worthwhile do go the 'EXTRASEAT' route and get more lateral space.