You will find that just adding tweeters will prove difficult to get you the sound you are looking for. Operating frequency and effency are hard to match with your OEM mid. I have modified a lot of systems using the OEM radio, and I would recommend you add a 4 channel amp to run your OEM speakers and add a sub with a small sub amp.

If you desire that you don't have to keep the factory radio you could do a double din with Car Play/ Android Auto feature. This alone will give you a substantial improvement in sound quality as most (I have a Kenwood) have time alignment and an equalizer to actor the sound to your liking.

Don't be afraid to visit quality area dealer, you can't hear products from an online site.