You can play house all you want, but nothing brings a couple together like a major financial commitment. If it's in your budget, look into purchasing a home together. It's a long, involved process that will require you both to closely examine personal preferences, make compromises and secure joint financing. If that's not possible, perhaps another major purchase, like some new furniture or even stocks, will help you feel more financially and emotionally independent from your in-laws.
Whatever you decide to invest in, it'll give you the opportunity to research, discuss your options and make decisions as a unified couple. When he picks up the phone to get Mom's opinion, remind him that the decision is yours to make as a twosome, not an affair for the entire family. Since his mother loves and supports him unconditionally, remind him that she'll undoubtedly adore the choices the two of you make together.