With size 11.5 feet that are still growing, a wide board is your best bet. There are a lot of wide options out there. Check the sites for GNU, Rome, Burton, Nitro, Ride, K2 and a bunch of others for starters. They all have a few wide options that fit your needs.
I have size 12 boots and I ride a GNU 11up. It's labled as a wide freestyle board but is a pretty good allround board and handles pretty well at high speeds. It's not real flexy like a full park board. I'd recommend it based on what you said you want. However, there are a ton of other options out there so just find what you like, and what you can get a deal on.
Depending on your price range, also check out GNU CHB-wide, Rome Flag or Manual, Ride Fleetwood, Decade-wide or Dose, Burton Bullet, Royale(mid-wide) or Custom-wide, K2 After Black....