UE has even introduced an IEM that you mold to your ear after receipt, using what they call Lightform Technology in their UE Fits. /u/SarcasticJustBecause these are probably your easiest entry into custom-fit earbuds. Source: about 1 year ago

You can also tryUE Fits, or Logitech G-Fits if you want something with better bluetooth and latency performance. These will mold to your ears, and they also come in smaller tip size and larger tip size so you can try those. Source: over 1 year ago

These seem to get good reviews: https://custom.ultimateears.com/products/ue-fits. Source: almost 2 years ago

I fly, very regularly. I wear these earbuds to block out sounds of other people and listen to audio books at home for hours while doing chores. They heat up and mold to your ears when you set them up initially. https://custom.ultimateears.com/products/ue-fits. Source: almost 2 years ago

UE Fits have really good fit especially for gym, tho don’t have wireless charging or ANC (although there is some passive sound isolation due to the unique snug fit). Source: almost 2 years ago

I own Bose QC earbuds, Bose QC 20s and Apple AirPods Pro, but unfortunately none of these seem to totally block out the sounds, especially the bass, which I find especially irritating. Source: about 1 year ago