I'm struggling to picture what you could possibly be doing with your posture to cause damage to your neck with even the heaviest headphones. Whatever it is that you're doing, the headphones are not your problem.

Suggestion for this: Sennheiser 6XX series are very lightweight, open cans (thus no extra pressure in the ear, but people may hear your music around a little bit). About ~$200 these days, and these used to be world's best a decade ago.

I can wear them all day long, even when the music or video ends I often don't even bother putting them off...

I just loathe the wire but sound quality is so good it's not even funny to compare with equally priced Bluetooth cans.