help needed with boat

In terms of Lasers, you might want to try the Laser 16 or Laser 13.

As above, try and get a test sail in a rooster 8.1.  Otherwise you would be ideal for a phantom.

chaps, sorry put please read my post, I am looking for a single hander dinghy not a lazer 13 or 16 or 420. I am not a very good sailer so a phantom would be far to much for me to handle, I take it that the rooster 8.1 is for the laser 1 which i think would be going backwards from the supernova.

I cant imagine that putting a big rig on a laser is a great idea for a novice. The vareo may well be exactly what you want. It is a lot more roomy than a laser - both cockpit and boom clearance . Although it comes with an asymmetric kite you dont need to deploy it til you feel you are comfortable. As a boat it sails pretty well, although it can make hard work of upwind legs. It is an absolute hoot reaching with the kite up. 

To be honest if you fall in regularly in a simple boat like a Supernova you would be better to gain more on the water experience before you consider changing class. Almost anything suitable is probably going to be as if not more tippy that a Supernova.

Re suitable single handers for a 16 stone person - unfortunately there aren't that many.  The Finn and Phantom are the obvious ones. Some say the Blaze Halo may suit, personally I'm unconvinced the Blaze hull is a great weight carrier, great boat that it is for lighter crews. I haven't sailed a Vareo so can't comment directly, though there have been some very mixed reviews on here.

On the other hand, if not falling in is more important than anything else you should consider something with a smaller sail, yes you'll be under-powered a lot of the time but you won't fall in as much. There are many single handers that may suit such as a Solo, the big issue I've found with also being pretty big and heavy is to find a class with a decent sized cockpit otherwise you'll be cramped and uncomfortable.