There are lots of solutions that would make your first enemas more "enjoyable" by making them harder to hold. Ivory soap, as you said, is a good one. Here are 4 more commonly used ingredients:
1) Dr Bronner's Peppermint Castile liquid soap. It comes in a cylindrical shaped stand-up plastic bottle (several sizes) and looks gold in color. It's pretty much made for enemas and cleaning but it's made from a natural substance. You can find it in any healthfood store, most drug stores, and some grocery stores. Start with mixing about a shot glass of it in 2 quarts of water to see how it effects you. Increase or decrease the amount depending on how you reacted to it. It's always good to do a rinse plain water enema afterwards to get rid of the soap.
2) Vegetable Glycerine. This is a bit harder to find. Usually vitamin or health food stores. It's usually available in liquid form. You can start with a little more of this, maybe one and a half shot glasses per 2 quarts of water. Adjust according to how you react. This can also be found in a green "hand soap" looking bar at Wallgreens near the enema bags. Swish it around in warm water until part of it is dissolved and visible in the water.
3) Epsom salts. This is easily found in grocery, drug or health food stores. It's large granuals of salts that causes cramps and a need to expel. You would start with about 1 tablespoon per quart of warm water to make the salt dissolve, then cool the water down to desired temp prior to taking the enema.
4) Lemon juice (from a bottle). Add about 2 ounces of lemon juice per quart of water. Some people get a big reaction to this, some not so much. Adjust accordingly.
Don't use any commercial chemical soaps or chemicals for enemas (other than ivory soap). They could really damage your intestinal lining. Be careful. No other hand or clothing or dish soaps or cleaners!