A couple of things to note, what is your budget?
Out of all your equipment a mask is the thing you want to spend something on, there is no point in saving £10-20 to get a mask that isn’t as comfortable, this thing could save your life and most likely you are gonna have it on for more than a short amount of time. I would look into one of these 3, Proflex, Flex 8, or profiler, all of which are quite lightweight, comfortable and have some form of anti fog device on the lens
In my opinion get the proflex, since it is cheaper, and more comfortable, but if i were you, I would go to your local store, and try on every mask they have there, find the one that fits you best and that you like, its all preference
But if you really do want to save a couple of £ try planet they have the extreme rage goggles in cheap
http://planeteclipse.com/site/prodView.asp?prodID=2178
But check these forums, there is always a mask or 2 going through like the proflexs I bought not a week ago, but personally I would always by a mask new and never second hand, its just one worth it since you never know what could have happened to it, or if you do, put a new lens in it asap.