For the conditions you describe I would go with the shape like Jimmy Lewis Super Frank, Infinity RNB, L41 ST, or Tomo inspired shapes. They work great in mush but are also pretty good in bigger- shoulder or so - surf. I am 6'4 x 240 pounds and my go to board for small, short period waves is Custom RNB at 120l. Since you are coming from larger boards something around 130l would be perfect. I would avoid boards in 160l range as the high volume may be detrimental in chaotic wind driven waves.
Longboards don't really work in a short period small waves, which is usually the case for wind driven mush. You need a short but early planning shape - a groveler. I am a big fun of longboard SUPs but I would not use one in a short period mush. But if it is 15s+ 2 foot glass there is no better shape.
If it is often windy why don't you try a wind sport. Wingfoiling in 20+ knots is way more fun than SUP