CIEMs completely solved this problem for me. Like you, I could only stand foam plugs for a short period. Nearly 7 years ago now I got a pair of 4-driver CIEMs from Alclair, and they are still going strong today. I can literally wear them for 8 or more hours at a time without discomfort - this is a godsend for air travel. I put them in before boarding and they stay in until I’m back in the terminal.