I'm sure somone will write a good book on this saga one day, like they did with the Collins class shenanigans.
Before going to the French, the RAN wanted the Astute class but the Aus politicians wouldn't countenance nuclear. The tried to get BAES interested in doing a non-nuclear Astute but it never went anywhere. By the time they finally realised they had to go nuclear, they were too late for Astute, so need to go with Astute replacement.
'Steel, Spies & Spin' is recommended bedtime reading for anyone in the UK submarine business.
Also 'End of an Era' by RJ Daniels which has a chapter on Aus O class replacement. I lent that book to one of the senior British sub engineers involved with Collins and he said it rang true.