Yes you should use sea salt if it is not iodized. A normal saline solution does not get absorbed by the body while plain water does. A saline enema is less irritating than a plain water enema. If sea salt is iodized it is usually mentioned on the label.
You did not mention the size of your coffee enema nor the length of the retention. If your coffee enema is say 2 cups and you retain it for 10 minutes then you will only expel a part of the toxins and therefore a post cleansing enema is necessary. As your system gets cleaner and cleaner you will eventually not have to take the pre and post cleansing enemas. I, at present, do not take either unless I feel toxic. By the way I had the same problem with gas and experimented until I got relief. I hope it works for you,
Most doctors will not mention either of these additional enemas and neither does Dr. Sherry Roger in her books on detoxifying. She does give info on additional supplements that I have found quite useful. I have not tried the infra red sauna but I am considering going for it.
Please read my blog titled My challenge, link below.