My ear canals are quite large and I notices the bigger types of earfoam are only available for headphones with wider stems.
I decided to make shims to make the 5mm earfoams fit on my 3mm SE215 headphones.

Because I those headphones for sleeping and the Bluetooth adapter doesn't lower its volume low enough, I have also included a closed variant, which significantly dampens the sound, but doesn't sound too terrible.

Fot the people where that 2mm is too much (sleeping on their ears), I have included a shortened version, but you will need to take 2mm off your SE215 headphones for it to work.

I strongly recommend printing these in TPU 95A (or another flexible filament), as it latches onto the ridge on the SE215 with a gap on the inside.
(and the edges on the closed variant feel less rough)

UPDATE: Due to the finnicky nature of printing sub-mm holes in TPU, I have given upsizing the tiny hole and succumbed to using a miniature hand drill to get the hole “just the right size” to pass a comfortable amount of sound:

https://www.printables.com/model/673681-se215-ear-foam-shim