I know this is a stupid question, but I'm not entirely sure what you do. Presumably.
1) If we replace with a gas oven , I buy the oven, get a fitter to remove the old one and fit a new one.
2) If we replace with an electric one, then same as above but I also need an electrician to run a new mains spur for the new oven, and the gas fitter caps off the existing supply
Or do new ovens come with the option of a fitter.
To compound the problem the existing oven is 570mm wide by 850mm tall which , it appears is no longer a popular size.
any general advice on what seems a bit of a logistical problem, would be much appreciated.