At last! After years of searching I've finally found someone who actually admits to watching the shopping channels ;-)
From that, you'll probably gather that I don't watch them, so I can't directly answer your question. I can say for certain, though, that the device won't be a dehumidifier. They take moisture out of the air. If the device requires you to put water into it, it's far more likely that its purpose to increase the moisture in the air. i.e. it's an humidifier.
While I can't find one which matches the description you give, Argos sell several humidifiers. Only one of the descriptions, however, specifically refers to using aromatherapy oils:
http://www.argos.co.uk/webapp/wcs/stores/servl et/Search?storeId=10001&catalogId=10001&langId =-1&searchTerms=4150554&go.x=12&go.y=13
If that doesn't meet your requirements, try typing these numbers into the search box on the Argos page:
052/1297
052/1187
052/1211
(Or, if you've got an Argos catalogue handy, just see the bottom of page 577).
Chris