I like codeine, would be awesome to walk into a grocery store & walk out with a few boxes of codeine phosphate, 60mg pills, or even 120mg pills if they make them.
Getting back to your question tho.......350mgs a day of codeine is six of the 60mg pills, not much of a habit at all, & you want to get on methadone?
Do you really know how strong methadone is?
IMO, if you had a hydrocodone habit of 150mgs to 200mgs a day........or a 240mgs of oxy a day, I would say you could try methadone to see if it helped.
Question: do you think you will ever try opiates again?
If so, why would you ruin your tolerance with methadone?
Because after you've done methadone, codeine won't do jack for you.
Only thing I like about methadone is it lasts forever, you dose once when you wake up & don't have to touch it for over 24 hours most times.
If I could get codeine phosphate & as much as I wanted, I would never go to anything harder.......until of course it stopped working.......