Dwarf Gouramis can be prone to bacterial infections. They can be fine for months and then BAM.
For something small in the way of a gourami, a pair of sparkling gouramis could work very well.If the tank is relatively recently set up, I'd let your tank mature for a few more months though before adding them just to be sure everything has settled and is stable
The aforementioned Endlers are also a good choice, a shoal of 8 males would look very nice and will without doubt brighten the tank. I always think they look like a small kid went ballistic with a couple of neon pens on their skin
Or if you want something with a bit more personality, a group of 5 female Siamese fighters would work. They don't have the long flashy fins of the males but are equally as pretty IMO and very entertaining and friendly.