Consider just wearing more/warmer clothes to sleep in --whether you do the hot water bottle trick or not.
I've been bringing insulated clothes that I can sleep in because I don't like to take off my warm clothes before bed and then warm them back up in the morning. For instance, I specifically got down booties that have a cover that I can slip on to make the nearly inevitable trip to the bushes overnight, so I don't have to lose that warmth.
I'll be bringing warm clothes for evening and morning anyway, so I use them to supplement the sleep system. It's easier for me to vent my quilt to shed heat than to bring a heavier quilt.