FYI, don't stress about lifting the lid. If you need to look, look occasionally, and without regrets. The kettle won't lose the heat for very long.
There's a comparison posted here somewhere, someone will know what I'm referring to, that showed what happens to the heat compared to a typical kitchen oven. The reason the kitchen oven loses so much heat when opened is because you're opening an entire side of the machine, whereas with the kettle, where the heat's located, stays "closed" more so. Even with the lid off.