I have a rule - I don’t fly long haul economy for an employer, ever. Premium Economy is the minimum tolerable, and if it’s more than once a quarter, I only fly business. No exceptions.
I have the same Premium Economy rule nowadays, but I now have the luxury of being able to do that; earlier in my career, I didn't.
But yes, it’s about how often you fly. Once or twice a year on a midhaul day flight like Uk to east coast or Mid East in a good economy plane (qatar a350 for example) is fine. flying 30 times a year then just say no. It’s not worth the damage to your health.