S.G.
When I was 9 I came home form school one day and my aunt was in my room. I dropped my stuff off in my room and went to the kitchen for my after school snack, took one bite of snack and went running to my room because I realized there was something very different about my bedroom. My dad had bought me a canopy bed and there was matching curtains and bedding. It was AMAZING!!! It was all the more amazing because I knew the sacrifices he had made in order to buy me all that stuff. We were not well off, not even close. That was over 30 years ago...
I still have that bed but not the bedding. I keep it mostly because it reminds me how much he loved me (he died 2 years later).
I say surprise your son. He may not give you the reaction that you are anticipating but I think he will enjoy it.