It seems to me - unless I am missing something - that there aren't any really big fat detailed books about the Cromwell. I know there's the museum-published reprint of the Cromwell manual (with additional material by David Fletcher), and there's two Osprey books (one about just the tank and one "Cromwell vs Jagdpanzer IV"). And there's a photo/markings book by David Oliver. Is that it?
I'd agree. Definitely worthy of a study a la Mr. Churchill's Tank or Dick Taylor's books on the Valentine. A very under-covered vehicle, book wise.
The Oliver Publishing Group in Australia published Combat Camera 1 Cromwell and Centaur Author Ian Carter ISBN 978 0 9806593 2 0 Only 32 pages but as the title suggests full of photos.