Most of the dwarf gouramis in America over the past few years have become afflicted with Dwarf Gourami Disease. It is terribly unfortunate, but the sad truth is that many commercially bred Dwarf Gouramis end up dying within a matter of months for largely unknown reasons. This doesn't seem to affect other gourami species, but the dwarves in particular, likely due to overbreeding and irresponsible treatment in fish farms are vulnerable on a large scale. I don't know if this is as big of a widespread problem in the UK since it's possible that you guys have different sources over there, but personally, I don't plan to ever purchase a dwarf from anyone other than a private breeder until this is somehow resolved.
They also can be aggressive and territorial, not a great candidate for cohabitating with bettas, unfortunately, especially because they are also anabantids. I have had luck housing sparkling gouramis, however, with a half-giant plakat, but they are much more skittish than dwarves.