I want to improve my car engine performance with no basic changes

The best way to not make mechanical changes and be able to get performance and then even revert to stock for emissions if necassary is to get an OBD II based performance computer add on. There are several companies that make them and the best thing that comes with them is the ability to read and erase trouble codes.
Most computers are around $300-$400. However the cost of an OBD trouble code reader is $150-$500. So, it offsets the cost and you get the ability to change performance parameters.
Try horsepowerfreaks. Com or summitracing. Com for sources to find one for your car.

The first things to do are to get an intake and at least a cat-back exhaust if not full exhaust and even a header if you can install it. You have the coice between a cold air intake or a warm air intake. If you live where it rains and puddled water will find its way into your federwell, pretty much anywhere but Califormian or the desert, a cold air intake will suck water into the motor. You can get by-pass valves to help with this but they don't keep all the water out and then they take in un-filtered air. The best choice, and it is only rated 1-2 HP less than cold air, is to get a warm air intake which stays in the engine compartment. It will give you a smoother intake tract, a better filter that is usually a lifetime warrantied filter and it will bolt right in. Don't scrimp on getting a cheap one. The best ones are; AEM and K&N. There are others and the places I gave you for parts only carry the good stuff. As far as exhaust, if you live in California or plan to, you have to make sure you get CARB legal stuff. Getting a header and exhaust all the way back is expensive but will give you the most bang for your buck as far as engine breathing when used with an intake. Again, go to Horspowerfreaks and they will probably guide you towards the best combination for your vehicle and keep you emissions legal.
Don't get into injectors and stuff like that as you can do a lot with the stock ones and changin them can cause issues if you don't have the need for them. Only highly modified motors really need bigger injectors.
If you want to tune your air/fuel ratio once you get your intake and exhaust, get an adjustable fuel pressure regulator and a wide band air/fuel ratio gauge. This is the best way to get the most out of your injectors as the proper air fuel ratio will give you performance as well as give you better gas maileage. Biger injectors can actuallly take power away and waste gas.

Platinum is the next to the best plug. NGK is really looked at tas the best plugs on the market. The top of the line pulgs are Iridium.
They will allow you to get a better and quicker more complete burn of the combustion charge in the cylinder.
To get the most out of them, you could get a higher energy coil from MSD. Look into horsepowerfreaks. Com or summitracing. Com if I have not mentioned them for your application.
Then you could get some lower resitance pulg wires from MSD. The whole combination would give your ignition a higher energy spark. A weak spark is a huge power robber.
The plugs will come pre-gapped and you can put them right in.

I don't have a cross reference chart, but any reputable retailer shoulkd be able to tell you. You might try to see if there is a cross reference or application chart on the BOSCH web site. I know NGK has one, I am not very familiar with Bosch.
Just make sure you get the correct application and heat range for your engine. They should come pre-gapped.

Go to the NGK web site and look up the specific plug for your car. Your local auto parts store should have the correct plug number in their system and be able to provide you witht the proper plug. If you do not have a parts retailer that you trust you can try going to, www. Carrepairlinks. Com. It is a compilation of the most reputable online parts retailers and services that I have found in my 25 + years in the business. You will be able to find that by using the links, not only will you be directed via catalog to the correct part but you will receive a discount exclusive to users as well. You can also use a phone number for Advance Auto and give them a code to get a discount.
When you get the correct plug, you can double check the fit just by holding them side by side, this happens sometimes when there are amany engines available for your model car. If they look the same then you do not have any worries. They already come pre-gapped to your engine.