Ok great, that gives us some room to play with.
What sort of books does he like? My DS is an absolute bookworm so I have a whole host of recommendations I can make on that front!
With regard to Stationery, Smiggle can be a bit pricey but tends to have some ranges which are 'boyish' and they sometimes do bundles which are better value for money. Paperchase also do some good pen sets which are quite neutral on the gender front.
If you're looking for a bigger gift them maybe a Kindle and a subscription to Kindle unlimited would be good if he's a reader? Lego is always a winner, perhaps go for some of the lego Technic stuff as he's getting older?
Also I would suggest board games, Some adultish ones though, like Settlers of Catan or Carcassonne, which are classics. There is an incredible board game called Volcano Island Countdown which I've played with a range of ages of kids and adults and everyone has enjoyed it, it's a great game as all players work together to beat The Game however the timer/countdown can make things a bit tense so depending on how your son copes with tension and time-pressure may or may not be right for him.
If he's in Minecraft then there is a pretty good Minecraft card game which would maybe be a good bridge into the world of table top games rather than video games.
If he hasn't already read them then the Usborne Puzzle Adventure books are great. These ones not the young puzzlers as they'll be too babyish for him.
If escape rooms sound good then take a look at Escape room games which you can do at home and many are really great.