I don't have a bath, so can't test that theory.

But trust me when I say I have more-or-less tried everything as far as I'm aware. Cold showers. Hot showers. Magnesium etc.

2 other ideas:

1. Have you tried a weighted blanket? I bought one this summer as I don't have a/c but find it hard to fall asleep without the feeling of a big blanket covering me. I found this one[0] from Bearaby which is wonderful. It's weaved together so doesn't provide much/any warmth. Just a lot of soothing weight.

2. This article - "How to Fall Asleep in 2 Minutes or Less" - helped me fall asleep quickly: https://www.artofmanliness.com/health-fitness/health/fall-as....

[0]https://bearaby.com/products/tree-napper

I wonder if he's tried—erm, nature's original 2-minute falling-asleep method... Like, taken his fate into his own hands, so to speak

I have similar issues with sleeping hot. I bought a similar open-knit weighted blanket from yaasa this year and really like it.

Having a small fan blowing air over me also helps quite a bit (the Vornado 5303DC has a remote and can adjust in 1% increments which is very nice for adjusting temp a bit during the night).

He should fiddle with the thermostat first (low low low) but I agree with the fan thing, although its more of a white noise thing to me as opposed to the sensation of wind blowing (over) you

Sorry, is this an insomnia discussion or like a "I'm hot before bed" independant of how the sleep goes kinda deal?

I would advise against cold showers/baths/immersion as the will shock you into wakefullness and vigilance. Can't see how there's any evidence for that actually working. Its like saying "Ya, I turned my phone as bright and blue as it goes up to and I STILL couldn't sleep" :/