Transition to cows milk

[ChocOrange05]

DS is 1 tomorrow and from 6mo he has been having cows milk with cereal and the ocassional small drink of it (babycino's without the chocolate!). As he is nearly 1 I decided to start moving him over to cows milk for his bedtime bottle, he is currently having one BF in the morning and a bottle before bed.

Last week I gave him 3oz cows milk mixed with 5oz formula (Aptamil follow on) as I have heard this is a good way to make the transition. The following mornings after his BF he has been sick, he was a very sicky baby but this is a rare occurance now. I stopped the cows milk for 2 nights and he wasn't sick the following morning. On Friday night I tried the cows milk again to see the reaction and on saturday morning he was very sick - projectile vomiting milk everywhere (was v scary as he was lying on his back and it started pouring out and choking him )

As he has been having cows milk since he was 6mo I don't think its a dairy intolerence. Could it be the mix?

I'm not sure what to do now. I called the HV advice line on Friday but no one has called back [grr].

Has anyone else experienced this?

Thanks!