i guess when your friend said sleep train with formula, it means to give formula milk for all night feeds including 2am and 5am. i tried to give formula at night and it seems that baby sleeps a little bit longer. but i read articles before that there is no difference between formula or breastmilk at night. it is common for baby at 1 month to wake up so often at night for milk. after eating solids at 6 months, you will see a noticeable difference - baby can sleep longer without milk