I recommend that you not introduce many new routines into your son's life. Allow him to create the kind of bedroom he wants. Maintain the same daily routines. Be careful to spend at least as much one-on-one time with him, if not a little more, as you did before. Do everything you can to reassure him that your relationship with him is as strong and special as ever. As much as you may be tempted to slack off in the discipline department, he needs you to be the primary love and authority figure in his life. Your new husband should not be placed in a role that only you should occupy.
And lastly, try to maintain as much close contact with your parents as is healthy and possible. If your son has developed a close relationship with them throughout his life, he should not be made to feel that this closeness has come to an end because of your marriage. Stay connected to his emotions by asking him open-ended questions: "What's changed the most for you? Do you like our new apartment/house? What are you looking forward to the most when we move into our own place? Are you nervous or scared about the move?" As long as you put yourself in his shoes, you'll be tuned in to making this transition and his new life a good one.