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.
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....
Weeds, the show, immortalized it as "nature's Ambien"
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).
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" :/