Good question, difficult answer. Each to his own.
I'd keep it simple at first:
Implement mandated Requirement Scrutiny rules. They're there to prevent waste, and make sure you get the right kit/capability at the right cost. The difficulty is that various Ministers/PUSs over the last 23 years are on record as disagreeing; and MoD has largely ignored the concept ever since. Perhaps a task for Captain Mercer MP, if Boris gives him the job.
Do that, and an awful lot falls into place.