Thanks for the responses all -
I decided to get Minecraft Java edition based on the responses here. However once I got to the website I realised I actually purchased Minecraft in 2014. However, I had never migrated my account to the newer Mojang account system and couldn't login or reset my password. I emailed support and chased several times - it took from August 27th to October 7th (41 days!) to finally get my account back. Obviously we live in strange times but 41 days is really really long time to be locked out of a game - especially one of the most popular games on the planet.
Anyway I'll try to report back to see what my son thinks of the game! Right now he's in the middle of a Plants vs Zombies 1 phase but will try to introduce Minecraft to him very soon.