In fuctional terms I think you would be best served by removing the auto sear assembly, and replacing the selector with a semi-only safety. Functionally there is really no need to modify any other parts. The firearm could be changed back to select fire by replacing those components.
Legality is a whole different issue. I have no idea what the law would be in your area regarding what is an automatic weapon versus a semi automatic one. For example what you are describing is not possible in the USA according to the government regulatory agency here. If they allow a permanent conversion to semi auto only in your country, at a minimum you will probably have to weld up the hole for the auto sear pin in the lower receiver and cut the "tail" off the disconnector, in addition to using the semi auto only safety.
ETA: In the USA, all the lower receiver parts are modified from their full auto configuration to prevent full auto operation. The hammer has the sear notch removed, the disconnector has it's "tail" removed to prevent contact with a FA selector, the trigger is closed at the back to prevent the installation of a full auto disconnector, and the safety is milled so as to not operate the full auto parts. The lower receiver has no hole for the auto sear pin.