If you are made of money and in the UK, you can attend this course[0] which is all taught using Postgres, doesn't require being enrolled in the associated MSc, and will seriously up your game.
Talking about books, I'd say PostgreSQL Server Programming is especially worth to look at, because extensibility is the very thing where PostgreSQL shines.
I had a street fighting knowledge of Postgres. I picked up "Postgres Up and Running" which filled in a lot of holes in my knowledge. It was surprisingly good for an O'Reilly book.
It looks like you can take this module for £1850. That's about the going rate and should pay for itself in increased productivity/earnings.
(My employer recently paid a similar fee for me to take a far less impressive msc module at a uk uni)
Why would you ever pay that kind of money for a course which teaches things that can most certainly be learned by reading 2 books which might cost 100£?
[0] https://www.cs.ox.ac.uk/softeng/subjects/DAT.html