Not me no ive never mixed the two why are you planning to?
Kratom with opiates should not be a problem(for most). Start out with 2 or 3g prepared in a tea(smoking Kratom is a chore). Be sure to look up cook times, it has been a while since I made kratom tea but it does work. It also depends on the potency of your stuff.
But starting out with 2-3g should do the trick, its not a high dose even if the Kratom is of super high potency, if it is lower grade, you might need to bump up the dose to about 5g. Start small I have heard reports from people saying it has caused some unpleasant mental side effects such as anxiety or restlessness (nothing serious) most likely due to the fact kratom is very stimulating and can have too strong of a effect on certain people such as marijuana does this to certain people.