One year old & cow milk

Ok so my son just turned one this month, and I'm having the hardest time with him drinking cows milk. I refuse to give him whole milk because it really upset his stomach, i tried 2% and he refuses that and he will take a little of 1%. The only way he will take cows milk if I still put his left over formula in it.. like 2 oz... is this okay to do still at one years old? I'm having such a hard time with this, I just need advice... thank you!

--- very stressed out mommy