If you consider kratom an opiate (is an opioid, technically... but..) I think is doable, for me, in +4 years of use I've never went higher than 15grams per day, and most time I've used 6-9gpd, which I think it's a regular and acceptable pattern (which daily could lead to dependence, but, at least in my case, no health problems of any case).
For me this has been sustainable, now I'm in a taper, will hit 5.5 today, and tomorrow I'll start the last part of the taper, next weekend will have a very light withdrawal, completely manageable with black seed oil, kava, mucuna pruriens and ashwagandha (perhaps some other stuff like yohimbe or kola nut, but that's the basic).
I guess if you're strict with yourself you can get that with other light substances like codeine, not sure. A friend of mine uses light doses of tramadol without much trouble. I wouldn't do but surely it's not impossible.