So, I bought some travel mugs.
The first one had to be returned, it was a Bodum coffee press, which despite the claims made, is not leak proof and spews hot beverage at times. Also, the plastic was poorly cured and smelled unhealthy.
I had more luck with the next two models --- they are leak proof and rather good looking. And they keep the drink warm wherever you take it along with you.
My peppermint tea mug:
You can buy it on Amazon and it's called 'One Click Cup'.
(The somewhat ugly label wipes off with some gentle scrubbing)
My red tea mug:
This you can also buy from Amazon and it's called 'Forge'.
The loop on the purple mug is a nice touch -- you can hook this over a finger and so carry a lot more stuff than you could if you needed to balance a big hot mug, and you can set up a hook on the desk to hang the mug on as well, so it's not in the way and can't fall over.
Both cups hold 500ml, you can put them safely in your bag, they look cool and they fit into a standard cup holder in the car as well.
Either cup happily deals with a tea bag left in it, and the purple mug is also ok to use with loose Hibiscus or Rosehip tea.
Happy hacking with spill proof, hot beverages!