Intestate

I currently live with my girlfriend, my house is valued at approx. £300k which I own and pay for solely by myself, my total estate being in the region of £500k. I'd like a will that gives my wife the right to live in my house after my death until she either, dies, marries or want's to sell the house, at which time I'd like the proceeds divided between my children and my girlfriend in specific percentage proportions by one of your will writers, I don'tknow much about will writing could you write a will like this and act as executor?