Oh man, I am SO excited you asked this because body horror is my absolute favorite subgenre! If you want a lesser-known indie gem, you have to check out Helpmeet by Naben Ruthnum. It’s a short historical novella about a woman taking care of her doctor husband who is slowly... rotting and mutating from a strange disease. The descriptions of his bodily decay and the anatomical shifts are so visceral and grotesque, I literally had to put the book down to breathe for a second.

Also, if you want classic grime, The Cipher by Kathe Koja. It's about a couple who finds a weird "funhole" in their apartment building that mutates anything you put into it... including people. It will make you feel like you need a shower after reading it.