Formula to cow milk transition. Bottle?

Hi i have tried my 18 month old son giving cow milk but he is refusing he has taken cow milk in other forms like in porridge form, with corn flakes but as whole form in bottle he is refusing he has been taking formula since birth, some doctor suggested give cow milk with puree and dry fruit powder but in bottle it will not be possible and he has tasted cow milk with other things but i want to completely replace the formula with cow milk so that he can drink plain cow milk as he drinks formula, i have heard about mixing formula and cow milk so that babies can gradually transition from formula so i just want to ask is it safe like mixing cow milk and formula, when he will start developing taste i will slowly reduce the formula in bottle?