School ideas to support an under-challenged child

Hi parents, seeking some advice here and hoping to get some ideas based on everyone's experience and expertise.

My eldest is in Year 1 at a local CoE school rated Good, and is now not enjoying school because the lessons are too repetitive and boring, and he is reluctant to go. He is high performing in all areas of Maths, Reading and Writing (e.g. he finished The Hobbit by himself in 1 week and is currently on Harry Potter book 1).

We've stretch challenges and games at home but he is still spending a good 6 hours in school and we don't want him to dislike school. (My husband experienced the same when he was in school and was acting out heavily. The answer then was for him to move up a year, which is not done now and also not an effective solution in reality).

Apart from the academics, he is happy at school and have a good social group of friends.

We will have discussed things with my son's teacher previously at parents evening last term and my son is getting lots of extension activities once the core stuff is done (e.g. more complicated additions or looking up words in dictionary to enhance his sentences), but because he's left to his own devices on these, there's not much motivation.

My question is: what else can we suggest and work with the school to implement?

I get that locally funded schools won't have the resources like private schools (which isn't off the table but from a financial, logistical and social perspective we see it as a last-ditch option), but hopefully there'll be something in-between!

TIA!