The urea cycle is predicated on the activity of several amino acids, namely arginine, ornithine, and citrulline, and aspartic acid can also feed into the urea cycle. My first choice would be arginine. However, it's best taken early in the day because the nitric oxide produced by arginine inhibits the enzyme L-tryptophan hydroxylase, which may interfere with sleep when taken in the evening.
Ammonia is very alkaline.
In this way, your body may actually be producing ammonia in order to protect itself. In such a case, you would not want to add fuel to the fire by taking any of the above acidic compounds. I cannot, of course, make recommendations, but these are a few biochemical considerations that I hope may be of help.