Honestly, if you're not a big hiker, I wouldn't do this.
You don't know how you will respond to heat, and if you're on any medication, overweight, or have an underlying heart condition, this could be very dangerous.
I say this having been to the Death Valley area. We stepped out of our (air conditioned) car, and it was intense. Not just the heat, but the intensity of the sun, was like nothing else I've ever experienced in Europe. I've been on holiday every year to the centre of France in midsummer at 40 degrees, but the lack of any shade means you have literally no respite. I almost physically felt a sensation of shrivelling and dessicating in the sun.
I would definitely play this cautiously. A temperature of 30 degrees combined with that relentless dssert sun had me lightheaded within moments. 😬
There are other ways to enjoy the beauty and adventure of this part of the USA. It'd be a shame to waste it in an (expensive) US hospital. Or worse. 😬
If you must go, please tell us youre going with a local guide. Brits are notorious for underestimating heat - look at Michael Moseley.
If you do go, make sure your travel insurance is comprehensive and that you're covered for adventure sports.