I was messing around with making piston doors and I made this:
It's 3 wide 3 long and 4 blocks high. I was wonder if there is any door smaller, or if this design is already in use. Also, it needs to have glowstone a block that doesn't cut off power in those two spots since redstone can travel through it, but you can just place another piece on the other side for decoration.
I might make a video on how to build it, but it's very simple and can be made just by looking at the images.
The pressure plate should be powering the block it on and that will power the redstone which will power the other block to toggle the torch. You just have to use a nonconducting block to prevent the plates from powering the piston directly.