I had tried lots of sippy cups but my 3.5 years old toddler did not want to give up the morning milk bottle until I came across a very American invention: the travel mug with a silicon lid. It worked for us.
The retail is between GBP 7 (Tesco) and GBP 15 (Amazon), in double walled ceramic material or even plastic.
What I like about them:
1) They come in different designs, colours, characters or animals. Make your toddler choose one they like.
2) The lid is soft and nice to chew on.
3) In general they hold up to 240 ml of milk, perfect for toddlers that still like to drink a lot of milk in the morning.
4) The lids don’t leak – even if your toddler is still not perfectly awake, the risk of bad accidents is dramatically reduced
5) It’s a grown-up thing, and they like it.
6) Can be used with the lid or without the lid and can last for years.