Hi Vanessia,
Sorry to hear about your sleepless nights, its the same here. So I totally understand where you are.
I did the mixing of formula and cows milk for about 10-14 days. Ds normally takes about 6oz of milk. SO I started with 5 oz formula and 1 oz cows milk, for 2 days then increazed to 2 oz cows for about 3 days then half an half for another 3 days and so on.
The transition was no problem at all.
I don't give fridge cold milk, I actually put say the 6oz in the microwave for about 40 seconds (in a glass not the baby's bottle) just to take the edge off. Although sounds like almost everyone does straight from the fridge.
the transition was a lot more smoothr than I expected and I am so happy to have done it, life is so much easier.
HTH
Mukta