Full cream milk can be used to make it more rich and creamy.
The amount of seviyan/vermicelli can be decreased or increased as per the liking. If you add more vermicelli the consistency will be much thicker.
You can add saffron or rose water to the kheer.
Nuts can be added as per your choice like unsalted cashews
Kheer tends to be thick when cooled. If you don't like thick seviyan kheer then add some more milk to the seviyan kheer.