Depending on your situation, you don't necessarily have to include your son. In fact, if she's a stay-at-home mom, NOT including the baby would be a nice day out for her. Being stuck at home all day with the baby is mind-draining. Let her do something adult with you (I don't mean dirty, I just mean a movie or nice lunch).
Also, some women really like the bath oils and stuff, but a lot of women don't. If your wife doesn't really do bubble baths and stuff like that, but you'd like her to do something pampering, maybe get her an appointment at a spa for a pedicure or facial or massage. Remember what I said about getting out of the house. As long as she's at home, she's at work. It's a treat to get away.