Chocolate gouramies need soft, acid, preferably tannin stained, WARM water (I talked to someone who has spawned them at 94 degrees! They need 80 or higher) and often live or frozen foods (chocolate gouramies are more willing to take prepared foods if kept with non-picky schooling fish); further, chocolates get closer to 2-2.5 inches (not huge by any standard, but seemingly a touch bigger than what you're shooting for). Much easier are Heterandria formosa...not at all colorful, but they are EXTREMELY hardy, not even slightly shy, and breed easily. The desert goby is another very hardy, easy to breed, bold fish that you can keep a pair or small group in a tank of this size without a heater...just make sure they have a good lid (they JUMP!). Currently I have Nothobranchius guentheri killifishes in a standard 10 gallon (the dominant male is just short of 2 inches), and they have given me no troubles (just hatched some of their eggs Thursday night...these things are among the easiest fish to breed in existence as long as you remember they are annuals whose eggs need to incubate in damp peat for a couple months. I regularly see them futilely spawning in the tank's gravel).
EDIT: Before you suggest it, don't go for licorice gouramies, Parosphromenus...while they are far from fragile in my own personal experiences (right now these 'tropical' fish are at 64 degrees and aren't the slightest bit perturbed, they've never given me disease troubles and even the fry aren't flinched by water changes) and are superb for 5 gallon and larger tanks, they need very soft, acidic, tannin stained water (PH of 3 isn't too low for these fish! Mine are in the mid/high 4's, 0 KH and GH and TDS of 20-25ppm), live foods, and since all are endangered in the wild they really should be kept alone for breeding (which they do erratically).