Re: Cost is the smaller concern
Wrong way around AC.
Within most organisations, it's only a very small number of niche users who need Windows.
The majority of "line of business" applications (email, ERP, CRM, etc) are genuine web apps these days, and work on any HTML5 browser.
MS Office 365, Google Apps, Libre Office and MS Office are all interchangeable for almost all users.
So most functions are in fact OS agnostic.
There will be a few specialists where the software they need is only available on one specific OS - usually Windows or Mac.
Then there is specialist hardware like MRI scanners etc, which runs whatever it runs (often Windows, Linux, or VXWorks) and the manufacturer is responsible for it.
And finally, if you are a big enough customer, the specialist software will be ported to the platform you demand. The NHS is definitely big enough...