I’ve used about 10 different boards (lengths and shapes) over the last 3 years, and have settled on a 10’2” as my all around board.
I’ve tried converting an old 9 foot slalom windsurf board for high performance SUP,..but the tail rocker is too flat. ( sorry JL)
The surf industry has spent years refining long board rocker lines,..the rail shape and rocker are critical when your holding the high line trying to make a critical section on big wave!
I’ve found a 12’ board is faster with its longer water line than say a 10’. They also track better making for less “S” turns while paddling. In the waves 12’ is more board to throw around,..but a good shape can still surf really well. The only negative in surf for a big 12’ board is the nose “throws” you back when punching through white water. A 9’ or 10’ is much better for paddling out, the shorter nose seems “punch” in the foam, rather than throw back.
The smallest board I currently use with limited control is a 9’ quad fin. Really fun is smooth clean waves,..but very unstable in any chop.
I think for your first board,...get a stable board with a proven surf shape. If you go too small, you’ll get frustrated (especially in the surf).
My conclusion thus far: SUP in surf 10’. Flat water: 12’.
A good allrounder may by 11’.
( I weigh 195 )
Some great websites on SUP: