Variable temp kettle AND whistle?

I need a kettle with variable temperatures and a whistle. This combination is impossible to find it seems. Hoping someone here has a recommendation.

My boss and his wife are just getting into tea, and she really wants a kettle with a whistle. But I really want to get them something with variable temperature so that as I introduce them to more tea, they can brew it at appropriate temperatures instead of just boiling black tea.

Thanks so much!