A thermos?
+1
We usually only need hot water for a cup or 2 of coffee in the morning so we didn't use an urn.
Instead, we used to keep a kettle on the hot plate over Shabbos but there were issues with fleishig/milchigs so we bought this:
https://www.amazon.com/gp/product/B09KMHL64M/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1It keeps the water pretty hot and its steaming when you open it in the morning.
I make a cup of coffee in a paper cup and its hot enough for me. My wife makes a cup in a ceramic coffee cup and its hot enough for her.
Of course we fill it up with boiling water before we fill it up for Shabbos so its as hot as possible.
Also, the summer, where Shabbos comes in 6:30+ will of course be hotter than a 4:30 winter Shabbos, but not so much.