I can bring the headphones I'm using to mix with at the moment, that sound like a pretty good plan. The gear shop does have a room for demoing monitors which isn't that small and has a little treatment on the walls. All the monitors are crowded around an imac and are on different levels so you can just move the height of your ears rather than a whole bunch of speakers.
I was thinking of a prodigy tune, a dubstep tune, some old soul, a couple of my mixes and maybe some dj shadow stuff. Am I right in thinking that I only need to test out the type of music I want to mix/produce?