I have the Fire HD 8 along with the charging dock and you might want to consider getting one next time it goes on sale. It comes with a kind of case for the Fire that has Pogo pins on the back and when I set it in the dock it charges. It works pretty well.
It does add more than a little weight to the Fire and the little case is useless for protection and I don't think you could use a real case with it on. But I don't normally bother with cases with my Fire tablets. I think of them as disposable.
Barry