hiya
Since Am was born ive been sterilising 5 bottles at a time, putting boiling water in, leaving to cool, and i add formula as and when for each feed. I bought some pots from asda that are divided into 3 so you can take formula either out and about or up to bed ready measured.
Luckily Am has her bottles at room temp so never needed to warm them, been doing this for the past 11 weeks and she's fine and putting on plenty of weight!!
Hope this helps