Our ds has just started on formula at 4 months. We have the Tommy Tippee bottle which should indicate when the milk is too hot, but the indicator is permanently pink, even when cold (I think it may have got damaged from using near boiling water). How would you describe the feeling of milk when it is at the right temperature? I know you should be able to tell by squirting some onto your arm, but what is the difference between warm and too warm??
I always squirted it on the inside of my wrist - if I couldn't really feel it, it was probably about right (as would have been about body temp). If it actually felt warm, I'd cool it more.
DS never minded it cool though, so I'd always err on the side of caution.
If you can, try and get your DS used to room temperature milk. It's very useful when you are out and about just to open a carton and empty it into the bottle, rather than worrying about having to warm it.
Wrist or inside of elbow works too. You shouldn't feel it if it's right. I also cooled rather than heated when supplementing and baby was only a newborn. I made up the individual bottle and then held it under the cold tap for ages, sloshing it around.