Looking for advice on best way to keep temperature of water when preparing tea.

What I tried so far

Electric kettle without infuser

Issue: Because I want to measure amount of water I go from Kettle to measuring cup which brings down temperature (measured 6 to 12 degrees drop) from just pouring the water in the measuring cup

Microwave

Issue: Have figured out duration + amount of water to get temperatures I want, but temperature drops the second I put the tea bag and can’t use loose leaves with this method

Kettle with tea infuser

Issue was more of a specific kettle than the method. The Kettle I first tried was somewhat wide so would have to put about 4 cups of water (32oz of water) for the water to go high enough on the container to get to the level of tea leaves. I think this will likely be the best method, just have to find a better kettle for smaller amounts since it is the only method that can keep the temperature closer to recommended temperature during the steep time. I figure one could probably also use a pot, but probably would be more of a challenge to keep temperature around a fixed level.

Brewing time question: All the temperature recommendations for different teas is that recommended time at start of steep or recommended temperature for the duration?

Reading a few articles online mostly confirmed that an electric Kettle with infuser is probably the best way to go. Any good articles with practical advice, or books, you would recommend? Lots of the articles online are somewhat generic and pretty much most have similar info.