Back in the day when I had a cd player and speakers lol. I had a pioneer headunit, pioneer door speakers the same as standard and poineer 6x9's in the shelf and tbh after a few days playing about with the settings it sounded really good!
I've had cars in the past with subs etc.... but I was very impressed with the set up I had in the
Ibiza, even had people check my boot because they wouldn't believe I didn't have a sub or amp in the boot.
So I would say get a set of door speakers (same size as standard) and some 6x9's with a good headunit and then it's happy days. Sounds amazing inside the car.... I'm not a fun of letting everyone on the street hear my music playing so I was happy wth it