surf sup or race board ?

flatter rocker and wide nose and tail imo.

Not a corky high volume board though... so many guys oversize this style of board and it ends up being a nightmare in chop as the rails sit high in the water... i'm thinking bodyweight + 15-20L at most.

Also, you don't want too short a board... you end up feeling like you're on a rocking horse, which isn't much fun.

Surface area on the water and how volume is spread seems the most logical consideration .

I've a Smik hipster twin Longboard 9'2" X 29 and it's very stable in chop (I don't have amazing balance either). I agree with the comment above about not too much volume. Corky is not stable. The board needs to settle into the water. I don't think a board needs to be especially wide if it has a Longboard styled round nose and the right volume. Less width also means less curve in the plan shape (in a longer board) which is more stable.

I've also also experienced too little and too much much rocker (particularly nose rocker). The board I had with too little nose rocker just dove into the back of the chop and was impossible. The one with too much just pushed water and was a dog to paddle.

Short answer is get a Hipster Twin Longboard. Your time on water will double!