green curry paste but no coconut milk
You can use light or heavy cream (19 - 35% fat)--it will be tasty but different. Coconut milk is about 25% fat, so can use a mixture of 2 parts heavy cream and 1 part milk (more or less) to mimic that.
Generally, it is best to fry the curry paste for a few minutes before adding the liquid--this rounds out the flavours nicely. This is usually done by taking some of the cream on the top of the coconut milk, heating it in a pan with the curry paste over medium to medium-high heat, and cooking until the oil separates out (maybe 5 minutes). You won't be able to to this with cream, so I would use some butter or vegetable oil for this instead.