Here's the post that made me research everything I could about IEMs for the next several days.

I ended up getting Truthear Hexa - they are said to perform exceptionally well for their price, even accounting for their date of release (IEMs are improving sound quality to price ratio every year). The only two things that I was somewhat wary of are that their nozzle that goes into the ear is bigger than usual and that people were describing them as "boring" and "somewhat lacking bass" (which is not actually a problem when equalizers exist and the user does not use iphones).

After getting the ears somewhat acclimated to wearing IEMs I tried different random tracks. Turns out that the tuning was perfect for me - similar to what I set on over-ear headphones, even (which are bluetooth headsets with ANC, and so have pretty usual tuning). Of course I could hear small details that went unnoticed before, Hexas are great at that.

Then I put on a track that extensively utilised sub-bass. Hexas do NOT lack sub-bass. They also render it good. I both hear and feel the music as it reverberates through my head. I feel the texture. To lesser degree it extends to regular bass, too, and it does not dominate the rest of the frequencies, nor does it lack.

I legit have changed what music I listen to because of this.

The only complaint is about stock eartips. Silicone ones hurt the ears, so I used foam, then got Dunu S&S. Now I almost don't feel that the IEMs are inserted, and they don't break the seal when moving the muscles, it's pure bliss.