Probably the nadir of music genres. Here's a recommendation out of far left field to accompany your Merle Haggard pilgrimage: Johnny Paycheck (yes, he's most famous for "Take This Job and Shove It"--which he didn't write--but that's a minor blip in his career). Start with his first real album, "The Lovin' Machine" (here's an AllMusic review to whet your curiosity: https://www.allmusic.com/album/the-lovin-machine-mw0000864851#review

Paycheck once sang with his idol Merle Haggard when Paycheck was in prison, and he later recorded a Haggard tribute: "Mr. Hag Told My Story" (AllMusic review: https://www.allmusic.com/album/mr-hag-told-my-story-mw0000057511#review

Working through Paycheck's albums is one of the wildest rides you'll ever take, and one of the most rewarding in my opinion.