I now have one of these:-
A Bodum Stainless Steel Travel Vacuum Mug
Once filled and locked, this thing is leakproof, which is good as on my bedside table (on wheels), it might be prone to falling over. As it’s going to be full of milk, that’s a bad idea. Filled with chilled milk at bedtime, it will hopefully remain cool enough to prevent it going off overnight, so I can use it to take my early morning meds, at 06.00, which badly need a buffer (the red top can be completely removed or the centre can be unscrewed for a drink-through facility) :-