You are not alone. I started with IEMs a very long time ago. Loved them but I could either get great isolation and sound, or not have my ear canals screaming in pain after a couple hours. Regular IEMs are based on the concept of average ear canals in shape, with some variation in size. Some people (raising my hand) have oddly shaped ear canals. Mine are very oval, lots taller than wide, and almost rectangular.
Eventually this led me to custom tips. Etymotic had a program where they'd subsidize the cost of having custom tips made - download a form, get your ear impressions, send them off to the mold place with the form and get a discount. (They don't do that any more.) Having custom tips was WOW. I got spectacular isolation, with comfort that ran to 5-6 hours. (Never really tried more than that...) Even nicer, it made the Ety sound better, because of the flawless isolation and because they go much deeper in the ear canal.
You can still get custom tips made for Etys. Probably $60 for getting impressions done, depending on where you live. (I live in an expensive area so I had mine done when visiting a friend in a less expensive place.) The custom tips were $150. The custom tips for Etys will work on a fair number of their IEMs, but not all. Still, it's not like if your earphones die, you got nothing.
That got me into the world of pricey custom IEMs, but since I traveled 4-5 days a week, sometimes on 22 hour flights, I treated it as an indulgent treat for enduring too much travel. If CIEMs die, you've got near nothing. Massdrop does great deals on CIEMs from time to time, but really, even with a sale it's not cheap. But, if you're in a job where you need to wear strong ear protection, and you like listening to music (like flying to Singapore each month) worth considering.
ACS Custom does tips for many more than Etys now. Poke around on their site. A few IEM companies now also will offer ways to get custom tips.
I still have and love some non-custom IEMs, because often I know I'll be listening for a limited time - gym workout, mowing the lawn. I have two different MEE and love one of them, like the other a lot. If I could get custom tips... I'd click to buy within 30 seconds of Massdrop posting the offer.