i recently upgraded my base system (no amp, no tweeters, paper speakers) on my F20 by purchasing a pair of 4.5 speakers & relevant tweeters from Aliexpress
+ the trims needed to install the tweeters directly from a BMW spare part dealer (but you can find the same on
https://www.leebmann24.de/ as instance) with very nice results
very satisfied with the upgrade
for a very base upgrade you could also install only the tweeters.
tweeters are called
2-BW-Tweeter-
629 model
mids are called
MidRange-BW-
635 model
for F20 & F21, F22, F23
Alpine labels (1 kit needed, it includes two badges)
65 13 2 230 426
only for F20
Left Door Trim with Tweeter slot
51 33 2 240 351
Right Door Trim with Tweeter slot
51 33 2 240 350
only for F21, F22, F23
Left inside trim 51 33 2 349 059
Right inside trim 51 33 2 349 058
mounted myself following some tutorials on youtube. first time it's a bit tricky to unmount the door trims, second door that's a bit quicker.