I'm returning to work in a month and have been breast feeding my DS, who will be 5 months old when I return to work. I am planning on expressing once a day (don't think I'll have the time to express more than once a day) & breast feeding in the morning before work and in the evening after arriving home from work, but I will need to introduce some formula throughout the day. Having not used formula before I'm not sure where to start, any brands better than others? How would I go about introducing the formula? Thanks!