Club World with a 2.5 year old.

We have a 2 and a bit year old son. Until he was 2 we’ve had a few great experiences doing Business with Qatar (rear facing Q suite with the middle wall down is a young family favourite !)

My understanding is he needs his own seat now he’s 2. - my wife and I want to travel CW, but I know he just will nap with either one of us, or sit next to my wife (they both fit comfortably on a CW!) - so we’re paying for 3 expensive seats but only needing 2!

Are the rules about a 2.5 year old having their own seat a BA policy, or an air safety rule?

There’s just no way he’d sit still on the other side of an aisle on his own. So 3 seats together in economy sort of works….

If he’s allowed to remain on my lap for takeoff and landing. Does his seat need to be in the same cabin, or can I buy him a cheaper seat that we don’t utilise.

Thanks for ideas.