I used to just take regular old bali/premium commercial and i found it is the best bang for your buck.
I'd put it in a coffee mug and add water and stir it (as good as possible, doesn't really dissolve) and drink the muddy liquid it makes, tastes bad until you get used to it.
There would always be some left in the cup after drinking so i would just keep adding a little water and drinking it until it was gone.
I wouldn't get it from headshops, you're probly getting ripped off price and quality wise. We can't tell you vendors but do a google search, there are a few good vendors with great prices out there.
EDIT: it may or may not help your sleep issues, it should help with

the wd symptoms and make you more comfortable, but like i said in another post.. it is a little stimulating. A lot more so than the hydromorphone you're used to.
I've found with opiates that hydrocodone and hydromorphone are more of a noddy type buzz than with oxycodone or oxymorphone which i could never even sleep when on.
But than again, kratom isn't in either of those categories so it might be different for different people.