I would also try to use a strain that has a more sedative effect, like Maeng Da Red or whatever works best for you. Mixing the powder with stem and vein powder in increasing doses until you have completely replaced the kratom with the stem and vein I have read many times is supposed to be the best way to avoid kratom wd.
Sorry, I can't give you a more exact model for timing these changing doses, I have never come across anything official looking nor have I tried it myself (well, I've mixed in stem and vein, but only because it supposedly gives a more rounded experience which lasts longer. I've never been scientific enough in my approach to taking any substances that I can't report that this is definitely true).
PM me and I will try and find more info on kratom withdrawal, never done heroin, but I know kratom wd can be pretty scary even with benzo analogues.