Will fly out of Frankfurt around the 15th back to BKK. Want to make a hassle free stop over for 2-5 days.

This will be on a return ticket of QR.

Any tips e.g. book hotel through QR , minimizing QR charges for stop over?

Stay in Doha or go to Dubai or?

Or think even further = Istanbul ?? Price wise probably interesting

On Qatar you get a free stop in Doha and that's it. Anything else would be a round trip from Doha to Istanbul or Dubai.

Above is right-would be self-evident to anyone.

You have to FLy in/out of Doha/Qatar for any visits-and that wont be cheap. Doha itself is quite expensive-also look into any visa-issues/rules. It would also be evident that just a short look at QR-webiste for any stopoverdeals or any of the plenty of other hotelbookingsites for what they offer there would give enough info.

IF you want another stopover, like IST-use Turkish-also plain obvious to anyone.

Of course you are right, but at times ideas come up which are out the box, asking never hurts. Don´t mind to spend some extra money.