Would defiantly agree with the comments above especially the wider and thicker, when your moving from a longboard your going from super stable to super unstable so make sure like they said previously get a wider board with ton's of foam.
- For your height and weight and your ability described I wouldn't go lower than about 35-40 litters in a board
- Shape can determine on a lot of thing but keep it wider in the node and tail than a usual pick
- Rocker is also a huge determining factor in catching waves you can shave off probably 4 inched of a board if you get the right rocker. so keep it really flat with just a little kick in the nose its going to help catch waves and have that similar feeling of stability on a longer board.
A lot of companies advertise their board and small wave grovelers or wide boys or great first time short boards
probably be a good place to start looking or even demo and see how they feel !!
probably good idea to start looking at 6'0-6'4