I've never really had a problem making a creamy cheese sauce - what method and ingredients do you use currently?
My method is to make a roux, then gradually add whole milk and then make sure to cook it for a good 10 mins or so to make sure the flour is well cooked out. Then, once the sauce is cooked and the right consistency I take it from the heat and add the grated cheese. I often use a mature cheddar (because I always have some in the fridge), but I'll also use other cheeses eg. mozzarella, parmesan, red leicester, or whatever else I have to hand. Sometimes a mix of cheeses is nice or other flavourings such as crushed garlic or herbs. Apart from the roux, I don't use fixed quantities....just use enough milk until the consistency is right, and enough cheese until it tastes sufficiently cheesy.