Hi there Mamma and welcome to this little group! Please dont be ashamed, we have all been there and its not our fault.
If you dont feel you can manage CT, then tapering is an option for you. You say you are taking about 400mg per day? Thats about what I was taking too. Are you taking over the counter or prescription? Either way, if you are going to taper, it is suggested to drop about 10% per week to avoid the awful withdrawals that come with CT. It will still take an awful lot of discipline to stick to your goal but it definitely can be done.
When I went through withdrawal (CT) I drank water, took berrocca and Imodium for the dodgy tummy. I have learned since that magnesium is good for helping relaxation and restless legs which you may or may not get.
This is doable and definitely life after codeine, I have been through countless withdrawals and am now over 6 weeks completely clean. Its wonderful. You say you are depressed and struggle with mental health? I think we all do in some ways. I promised myself this would be my last quit and have prioritised it over everything.
Keep talking and we can support you xx