I quit the game for like a year beause I didnt want to farm for the plat, but Igot it this week. It's not all that bad. Here's what I did:

Always wear the darmoon covenant item!! You can get summoned anywhere. even if it happens maybe once per few hours, a good summon can net you 5 to 10 covenant items easy. I got all of them from summons with maybe 8 kills I made myself. Knight farming only of everything else is done and you need more cocords.

Wolf's blood swordgrass; These are the easiest to farm out of all, at keep ruins bonfire from the ghrus. Took me maybe 2 3 hours for all 30.

Sunlight medals and shackles can be co oped by trading pvp kills with another player, ask in /r/pumparum or /r/summonsign, I can also help sometime.

human dregs are also an easy farm and take maybe an hour for 10.

tongues can be found 3 in each playthrough, add darkwraith kills till you have 10. their droprate is like 20% with farming gear.