I use the baby cereal Milupa for DS. He was BF at the time, but I couldn't express efficiently, so this one was suggested by my doc. You can use water / formula or BM to mix it and DS LOVES IT. DO NOT GET ANYTHING WITH HONEY IN IT, as it can cause botulism in babies. It seems that in your post, you are thinking of using an adult cereal. They don't have the nutrients specifically needed by babies, like Iron for example. The Milupa has a full day's source of Iron in a serving (7tbsp), and I used to split it up over 2 feeds (am and just before bed)
HTH
Beth