6.2 , 80kg , 13 US size ! The problem ofcourse is board! I tried a friend's board (same board but 157) and all became so easy for me! But I have a lot of toe draging so I have some hard takedowns. I never tried a rocker board also!
While it is true a board with scoop technology(I believe that is burton tech), rocker or even softer flex then a Twin can make doing a butter easier or sliding a rail board slide easier without catching an edge. Riders have been doing butters, boardslides, etc. on boards much stiffer decks then your Twin. Hell, half the veteran riders on here can do butters on decks like a Burton T6 or T7. Nothing equalizes out a rider like proper technique.
I might mention you might want to take a look at more then just the board. Stiff boots can be a detractor when it come to freestyle. A stiff boot can lock out your ankle and require more force to flex and extend. Binding angles and placement in relation to the working edge can effect performance as well.
If you are set on a new board with size thirteen feet you will need to stay on a wide board. Look for boards that have a flex rating under 6-7. Most likely you will need to stay close to the 161 length. Don't go smaller then a 157. A 159 will probably be about right, if not longer. The smaller you go the more likely it is for the nose or tail to feel like it is folding up underneath you when buttering. This leaves more a MUCH smaller range of error. Take a look at boots and bindings that are a little flexier too.
Boards you should look at anyways that I have had more then a passing experience with:
Neversummer EVO or Legacy
Burton Joystick or Hero(the Hero they do make in a wide now, but it will be a pretty different ride)
P.S. Since this is a park board remember it will be more likely to take damage. Spending a lot of money on a park board is like buying a Cadillac and then taking it to go to the demolition derby. Finding something that gets good reviews for taking a beating and that can keep on ticking.