There is an old thread that list orchid vendors in EU. As UK is a part of the free market within EU you should have no problem ordering from the Europeen vendors!
Orchids Vendors in Europe
For recomendations of plants there is alot of them. Some vendors lists temperature range for their plants but I usually dubble check them on the internet.
What about night temperature in your growing cabinet? Is the light the only heat source?
If the remperature fall to about 18-20 degree C by night there is alot of Pleurothallis, Lepanthes, Stelis and Masdevallia that should do fine. Bulbophyllum is more warm growing in general than above but should prosper in your temperature.