I have had a whole range of in ear bits. Hard acrylic would get hot, two different soft moulds were better but still sore, right ear especially. Then new aids with domes. After a matter of hours I called at the High Street chain that now had the contract and asked for smaller domes. I went from a 5 down to a 4 and the relief was immediate. These were double flanges and one ear canal was definitely smaller than the other. The opposite ear now became the uncomfortable one. I put a smaller dome on that ear.
The downside is slight, but unnoticeable to me, loss of amplification.
I then changed aids and got the phonak double flange equivalent. Again the pain would return after a time. Then I got the smaller tulip shaped ones and can now keep them in at long as I need.
Two downsides this time. Again a potential, but unnoticeable loss of amplification, but, more significant, I sometimes forget to take them out showering, swimming, or even going to sleep.
As I have said elsewhere, no matter how effective they are it counts for nought if you can’t keep them in all the time.