There are some options.
Noctua does make some small fans that would fit the original cpu cooler.
I ended up getting something with a bigger heatsink:
https://www.quietpc.com/ac-copper-silent3I believe it's the largest heatsink that fits the motherboard.
I removed the fan it came with, and put a noctua 80" on it.
If I put my ear right next to it, I might actually be able to hear it - on a good day...
This cooler is a bit tricky to find nowadays though - I think I found mine on ebay.