I use LiquiMoly 5W-40, however, being in Thar you should go for an oil with hot summer viscosity of 50. Visit LiquiMoly’s Pakistan website to check the oil types. Match them with the oil guide vehicle wise on LiquiMoly Germany’s website.
Mileage of the car is not dependent on engine oil. It has more to do with proper functioning and calibration of various sensors, spark plugs/ignition coil condition, injectors, fuel pump, fuel filter, air filter, etc. What is your car mileage? And what’s your driving style?
For dashboard/interior use a gel-based interior polish. Armorall has one and Meguair has one too. Apply them using a foam pad once you’ve cleaned the interior surface thoroughly. A good coat will last a few months.......may be less in Thar.