There are lots of trip reports on TK's J class. It's generally rather highly regarded and the lounge is also highly regarded. On the 77W that flies IAH-IST the seat map is 2-3-2 so if you don't want to be in the middle of two people be sure to select a seat otherwise. The shorter flight to Italy will most likely be on a narrow body plane with seats more like US domestic first class or with an empty seat between two regular economy seats.
If you've never been to IST recommend try it. It is a great city.