Sorry, I missed the part where you said you'd ordered a different thermometer.

Plastic wrap or aluminum foil won't make much difference - they're both impermeable. Although foil will let you it closer to the heat lamp. But honestly, the hole for the heat lamp is going to cause problems regardless. A radiant heat panel is a good alternative to the heat lamp, because it goes inside the lid and doesn't require a hole in the foil like the lamp does. They're expensive, but they work well and never need replacing like bulbs. You will need to do some minor modification to the lid to attach it.

You can try a different substrate, such as eco earth, that holds water better. Or even just make piles of it in a few place instead of using it throughout. Live plants help, too - plus they're attractive and good for air quality, and give the snake more things to hide behind.