100% agree about mesh suits. Brilliant bits of kit. There's also some "smart fabrics" = soak in cold water, wring out & it stays cool for much longer than soaking ordinary fabrics. I have a scarf but t-shirts are available too.

Personally I've found altitude doesn't help much. In Portugal at 2000m it was only a degree or two cooler. Not really significant enough when it was still 40+ C at the summit. And at altitude the sun is more intense so you burn easier & get sunstroke quicker, and there's no shade because its above the tree line. Best solution was to start early and get back to base before 2.00pm when it became dangerously hot.