Geo teacher here; my advice is do what you enjoy the most because you’ll work hardest at it and do well. Dont’t do something that you’re not good at as you’ll soon hate it.
Saying that; languages and humanities are seen as the tougher options to prove yourself. If you’ve got decent literacy these will be fine.
Coursework is going, might be worth reading the draft GCSE specifications on the exam board websites to see if he’s interested in them.
The school should have a parents evening about this, if not ring the tutor/head of year and ask their advice. They’ll give honest advice about what is best for your son.