Welcome to the forum Pazz,
And what a potentially complicated question you've posed! (But you'll certainly get answers I reckon!)
I suggest you take some photographs af the wheelhouse in question and post them on the forum to help us, but here's my comments to begin with.
It is, of course, certainly possible to reduce the height of a steel wheelhouse, or remove the top section (windows and above), and replace with a collapsible arrangement, (most frequently fabricated in hardwood).
However, to all intents and purposes, there's no such thing as a "standard wheelhouse", and any work you have done will require the invoilvement of skilled boatbuilders/fabricators if you are to achieve a competant and good looking alteration in keeping with the current boat's appearance.
I'm quite certain that some of our members will be able to make some recommendations on whom you should approach, but have no doubt that the project will cost many many £,000's, as the wheelhouse is the main saloon, (and therefore a reasonable size I guess) - I'd bank on the cost being in the five figure range.