Hi André. I have studied the DES mixture of choline chloride and glycerol as plasticizers to biodegradable biobased films, and I used the ratio 1:2 based on its weight (w/w). I believe that this could be the same for your DES mixture of choline chloride and urea.
The following link may help you understanding more about DES: Article Glycerol-based deep eutectic solvents: Physical properties