Yeah avoid nytol etc. For sleep as they can make some shptoms worse.
Good call in getting off the opiate train now mate!
If possible, could you not just say you have flu/sickness/diarrhoea and take the valium on days 2,3 and 4, and go to bed with your families sympathy, watching Netflix and being brought noodle soup and the occasional paracetamol?
Otherwise you could just replace your codeine with loperimide (aka immodium - don't get brand name though, just get cheap bangain buy or poundshop shit, it's exactly the same thing except 5 times cheaper).
Start with 4-5 tablets, and this should clear up all or at least most of your symptoms in a couple of hours. If not, take a couple more.
Take one tablet less every day or every other day, and you should be golden with a codeine habit.
Hope it works out pal!
Before I got a.big habit, I found the loperimide to be easy peasy! Especially if you've got vallies!