Cows milk does not have enough iron or the right types and amount of nutrients that are present in breastmilk or formula so it shouldnt be given as a main drink before 1 year. Just because your MIL gave cows milk from 6 months in the past doesnt mean it was the right thing to do.
However, from 6 months small amounts of full fat cows milk can be used with cereal, in foods, in cooking, etc as long as your lo's main feeds are formula/BM. (You dont need to boil the cows milk first)
If you decide to move to formula feeding you can choose to use an ordinary 'first' milk which is suitable from birth or to choose a 'follow-on' milk which is suitable from 6 months. The follow-on milk has a bit more iron (which can be constipating - although my dd was fine with it!) but is also slightly cheaper. If you didnt know which one to use, buy a few individual small cartons and see which one your lo likes best.
Good luck
Seona