He never minded one bit, accepted just fine that anything that came from a bottle was cold (as opposed to body temp). When I pumped breast milk
and had it for him in a bottle, I gave that to him cold as well. No complaints from him.
Anyway, moving him to whole milk (and now 2%) was no sweat in terms of the milk's temperature, as he was already used to it straight from the fridge. It sure saved a lot of time, too, not having to heat formula in the middle of the night.