I'm guessing that you are a young chap and hope you realize that adding a turbo is not a cheap thing to do properly and that your insurance cover will rise heaps depending on your age and history if your present insurer decides to continue with your cover
You MUST inform them of your intentions because if you haven't and have a crash they can refuse your claim and you will be up for both parties repair costs.
Things to look out for when adding a turbocharger to a non turbo car, some basic pointers. How to turbo a car, can you put or add turbos to any car and guide to how to install or add a turbocharger on a non turbo.
Best route is usually to source another same model with a turbo and transplant the engine, and there were a few Astra turbos through the years that could provide a donor engine and parts.