The rule of thumb for optimum blanket weight is 10% of body weight + 1lb.
I came across them with this article last month: https://www.theguardian.com/world/2018/jan/20/use-of-sand-ve...
Even if temperatures do drop overnight, I like that the sheet somewhat contains my own body heat and is relatively warm inside the sheet.
Of course, in the winter time I'll upgrade to a blanket, but I try to stick to the lightest possible one.
Quote from the article:
As one more example of the goodness of blankets, there has also been a decent amount of research about the calming effect of weighted blankets, which can weigh up to 30 pounds. Studies indicate that they can curb anxiety and even be used in the treatment of autism.
This triggered my memory. I heard it helped kids with Aspargers and ADHD too.