think this way: since he is your dearest son, you should know his habits and preferences very well. In fact, no matter what, don't think too much first, your gift is for him!
I think you should consider the following aspects:
1. Based on your understanding of your son, does he have anything he particularly likes, but his parents have never bought it for him?
2. What are your fixed habits? Start with his habits, just right, and have a clear goal. It must be something he likes and can use!
3. If you want to give something more innovative and commemorative, then it is a customized gift. Now there are many places that can customize such gifts in different styles. You can provide a photo of the woman and customize it, or you can engrave what you want to say to your son on it.
4. Does your son have any gifts that he likes very much, or a gift that he has always longed to have?