E.,
Wait the 6 months out. Here are the Cliff Notes:
1. The longer you wait to introduce foods, the better chance he has of NOT developing a food allergy. Some foods are better to wait up to 2 years, such as peanut butter and eggs. These types of food run a higher risk of food allergy when they are introduced too early, especially if you or your husband have food allergies.
2. There is no guarentee that putting cereal in a baby's bottle will make him/her sleep through the night.
Trust me...we started putting cereal in my son's bottle when he was 3 weeks old and now he's 19 months old and STILL doesn't sleep through the night. *sigh*
Breastmilk is all your son needs for nutrition right now.
However, if you do decide to put cereal in his bottle, start with a very minimal amount (say...a 1/4 of a teaspoon or less for a full bottle.) I used rice cereal and opted not to use the oatmeal or other flavors. Introduce it slowly and see how he takes to it. Make sure that if you are using special nipples (ones with a number system such as the ones that go with Avent bottles) that you do not clog the nipple with the cereal. You may need to go to a nipple with a larger hole. Be careful not to get a nipple with a hole that is too big and drowns your son when he is trying to drink his milk.
***Finally, if your son gets too full, (babies are known to over-eat,) you can run the risk of him choking, vomiting or even developing colic - due to the excessive gas and pain associated with the new foods, bloating, over-full tummy, etc.*******
I wish you the best.