In the Agatha Christie book Nemesis, Miss Marple is offered a milky drink at bedtime by Clotilde Bradbury-Scott, whilst Miss Marple was staying as a guest in her home. She declined to drink it- and good thing- it was poisoned!
In my own country, a hot drink at bedtime is usually hot chocolate. If Miss Marple had been offered hot chocolate, I believe it would have said so. So I did a little research and found a hot milk-based drink in the UK called Horlick’s. It is similar to Ovaltine in the US, but without chocolate- it is a hot malted milk beverage.
I purchased a tin of Horlick’s and found that I really liked it. I suffer from insomnia if I partake of caffeine late in the day, and I found it to be a nice substitute for cocoa.