There is no such thing as coconut essence. There is coconut cream (very condensed and very fattening) coconut milk and half fat coconut milk which is just 50% coconut milk and 50% water. If you want to do a proper curry with coconut milk (thai or South Indian) there is no substitute.
I've had great success using 'Oatly' when making curries. It's a sort of milk alternative but is bascially made from oats and water (sounds worse than it is)! It's more liquid than yoghurt so the chicken and/or vegetables cook in it. You can 'cream' it up at the end by adding some 0% fat greek yoghurt.
I agree entirely with 237SJ - I would rather have the real deal and be extra careful over the next couple of days rather than attempt to eat a red thai curry without proper, full flab coconut milk, I just don't enjoy it as much with any low fat version. I would rather make a different type of curry like rogan or balti which I think can be done with less calories/fat than skimp on the coconut milk.