Giving your child choices is one way to reduce the number of no's you hear from him. Also, encourage him to answer in a quiet voice, and coach him in some alternatives: "What's the opposite of 'no'? 'Yes!'" "You can say 'no,' or you can say 'yes,' or guess what's in the middle? You can say 'maybe!'"
Your life now:
The switch from crib to bed often ushers in an era of middle-of-the-night visits to your bed. If you're not up for sharing your covers, lead or carry your preschooler back to his bed and bid him a kind but firm goodnight. Don't turn on the lights, don't talk much, don't get emotional or otherwise make it a fun, daytime-like experience. You might have to repeat this routine multiple times before the nightwalker learns to stay in his own bed at night. The key is to be persistent and consistent.