Yeah, it's sounds like a "big" problem.
But since you're 16 your feet probably won't grow more, which is good. I'd recommend the following:
* Go to a good boot fitter, if you haven't done so already, and get a boot with a lot of shrinkage tech, such as Burtons. And make sure they're the tightest comfortable size possible.
* Go to the gym and gain some weight in muscles, dude.
Apart from making you heavier it will make you stronger and thus more able to control a bigger board.
* Some of K2's wide boards are quite wide, such as Slayblade: 159w waist 264, Raygun 157w 262, 160w 265. The Raygun isn't supposed to be too stiff so it wouldn't be unmanageable despite being above your weight range. It's fairly cheap and if you can find last year's it'll be cheaper.
* Rossignol One MagTek 157w, waist 264. A more high end board.
* Or you could check out Freestyle boards! Sized up they will be stiffer and you can use them as all mountain/powder boards. An oversized Freestyle board with rocker SHOULD work well in powder, if you set it back.
* If you can find last year's Burton Honcho the waist of the 155w is 264 and of the 158w 265. It doesn't get raving reviews, and since it's regular camber you'll have to work it a little more in pow. But hey, it's a full wide and has a sintered base.
And with that, I leave the word to anyone who actually knows something about this...