With this sort of thing it's extremely difficult to do anything beyond speculate roughly. We don't have the intimate knowledge of your tolerance and usage patterns to determine how exactly your taper should play out. In fact, even if we were managing our own detox from Heroin, it would be just as hard, as we never know the exact purity of our drugs, making it possible to make accurate conversions to other Opioids.
You really need to feel the situation out yourself. How you will do this is by initiating withdrawal and finding out how much Codeine is required to mitigate the most severe withdrawal sypmtoms. You will inevitably experience some discomfort during the experience, but if you do things right, you can get through the process with a minimal amount of suffering. I would avoid the Amitriptyline. I doubt it will do much for your symptoms.
The Pregabalin (Lyrica) is going to be a great asset. It works wonders for most people's withdrawal and has the added benefit of sharing no cross-tolerance with Opioids (that we're aware of), meaning you can use it as much as you want without having to fear an extended or reset withdrawal phase, unlike with Codeine or Morphine, other drugs at your disposal.
The Benzodiazepines will also be pretty helpful. Obviously tread lightly if you're to be consuming them with Opioids due to the potential for respiratory depression, no matter how unlikely that seems. Benzodiazepines also lack cross-tolerance with Opioids, so they're going to be pretty helpful in addressing a variety of symptoms. Restless Legs, Akathisia, Insomnia, general restlessness etc. Benzodaizepines are great for these.
The real key here is to not over-medicate yourself. You want to use just enough for you to get by and function (eat, sleep, etc.) when you need to. Could you give us some more details regarding how much Heroin you were using and for how long? I know it's not particularly useful information, but it will give us an approximation of how serious your habit is currently.
