I do sleep/nap on the side, and put a lot of weight on the ear or the bone in front of it.
I bought quite a few iems in order to find something confortable for sleeping with.
I had no luck with barrel shaped iems, even with small one like HifiMan RE-400 : the pressure make them dig in the ear, and any lateral move changes the sound or break the seal.
I did try the Soundmagic PL50, and it is indeed the most confortable of all : very small, flat, keeps the seal. Cable is so-so. And i'm one of those who dont like its sound
It sounds nice, it is bright, it's good with classical and jazz. But it has some heavy narrow peaks. When trying to EQ it flat, i had to use : -13dB at 2330Hz Q=24/0.06oct , -8dB at 6550Hz Q=8/0.18oct, -6dB at 8500Hz Q=13/0.11oct. And it needs some bass boost. As I like to listen to ambient electronica to drown out neighbours noise, I need some bass to make the sound "whole", and any drone in some frequencies (eq'ed down above) would hurt.
I spent quite some time trying to live with this PL50, but no, not for me.
I tried a few other flat IEMs : Meelectronics M6 (flat, but body a bit too wide), some budget JVC (not flat enough).
But my happiest finding was the
Jays T-Jays. I even bought each of the serie, in that order : T-Jays Three, T-Jays One, T-Jays Two.
General comment about the family, and why I like them :
They sound good and balanced. They all have good bass. The first days, with each of them, I thought the bass was too strong, but after a few days, I dont think that way anymore. The bass is there for my ambient, not overbearing, and the sound is good.
I can't wear them straight down as they are supposed to be worn : their big and sharp body hurts my ear. May be I just have small ears.
But cable up, they are the most confortable I had, and i can sleep on them for hours. Only downside is that channels are inverted (left on right, right on left). So, you have to not be bothered by that, or have a player that can swap channels (there is a patch for that for rockbox that one can custom build).
Also, their cables are quite small : 60 cm. Which I like ! I can just clip a sansa clip+ or clipzip on my chest, and sleep and change sides without messing with a long cable.
For an even better confort, I use them with comply T-200, inverted. Inverted, they sound better, and u can adjust the position so that the pillow pressure is distributed between the iem body and the tips' tip.
I'm so happy with them that I dont use better sounding IEMs anymore (re400, philips fidelio s1), even when not sleeping : the small cable and their confort are such a big plus.
About the differences in the family : Two is balanced, not offending, sounds good. One is similar to Two, with a bit less quality in the sound, a bit less clear. Three has some upper bass/lower mids enphasis than makes them a bit muddy with classical. I prefer the Two.