I'd negotiate a part-time roster, or seasonal one. See how you feel then, both mentally & physically. 50% or 75% should be possible for any company. Indeed, is it not they case they have to show why they say No? Seasonal, with 75% in summer & 50% in winter might also work for you. It's not so all or nothing.
I empathise and spent my last 12 years at 50% the normal rate, but also I wasn't an employee. For those years it was very tolerable. The thought of full-time as an employee is not an option. That is both the disruptive working life-style and the common degrading work environment created by those at the top. Considering how far the technology has advanced and modernised it's a great mystery why the management style has reversed and now resembles that of middle ages 'Lord of the manor' with the forelock saluting peasants, or the mill owning robber barons of the 19th century. But we are not alone in this puddle of poo. Many industries now use 'zero hour contractors', much to the distaste of some UK MP's who spoke out about the practice. I note they didn't offer any solution or legislation, just condemnation. No doubt the share holding lobby would urge them to back off. All the EU labour employment legislation has not protected against such an explosion of abuse. One wonders just what they do all day long in the ivory towers of Brussels.