Fellow mouth guard person, here. Mine is teeth grinding at night from stress, so not really TMJ related, but my insurance didn't cover my guard either. My sweet hygienist recommended:

https://www.amazon.com/Doctors-Advanced-NightGuard-Protector-Nighttime/dp/B0036WTV2C/ref=sr_1_26?crid=2KAKX4KK0RNCQ&dib=eyJ2IjoiMSJ9.hTIs-G-hq0V2S578T9POho6--PMJ1lko573oh_GmgSGvuKWmDXccIXu13qulzSksiyLyK-XSsiagtfiyEtLE1ZmBMJiRc_dA2zIENib4iuVELUqGqbgocZoG2kIBhmzNMsRJKSPam4WIuk8FGfbQN8J9tjsok3ukb_jRclAuJqe2H90ONzPUwKy0-Ggeoh0X0pEBtGkbI45lZyanoExDNhtfLHa2Yh2jWJKydO8axMjBIjmgSa6mPt58qaHiKLyBRXaifoTB-_uOE9CgfqKbwCQxK3hpw6Opp8ZpT1dD2fo.zde3ZWh6REG6soegZoSNAQRCATy98m6At4Lo42jvJxA&dib_tag=se&keywords=mouth+guard&qid=1713878966&sprefix=mouth+gua%2Caps%2C353&sr=8-26

I don't know if you need a special, special one - but this one has been great. I have it on auto ship and get a new one every six months or so and it's still way cheaper and suffices!