As far as I know, there is no special kind of coffee that is recommended , but the main thing is that you do not add milk and sugar to the coffee, whatever kind that you choose to drink.
Some people use artificial sweeteners, and others say that they can still cause an insulin spike, even though there is no sugar in the sweetener.
Using heavy cream is okay as long as you only have a cup or two and not using a lot of cream, because there are very little carbs in the heavy cream. Too much would break your fast, but during your eating window, you don’t have to be concerned about that part.
Some people also add coconut oil or MCT oil to their coffee, or butter, and this is called Bulletproof Coffee. It is similar to the bombproof coffee, which is coffee with heavy whipping cream added.
Sometimes, I also add a small chunk of cacao butter, which melts and give the coffee a really rich chocolate aroma and flavor.