A pearl gourami would be stunning in a mix of embers and CPDs. Pearls can be a bit shy, but they seem to open up more in a nicely planted tank with some surface cover. They grow to 4"-5", though not usually over 4.5".
Most gourami species are very hardy, though the various color varieties of dwarf gourami have become quite weak due to inbreeding, often living for only 6 months. The normal colored dwarf gourami might be a bit hardier, but in recent years their quality has declined and they often succumb to early deaths as well. Dwarf gouramis grow up to be about 2".
Honey gouramis are one of my favorite fish. They are a small species, maxing out at about 1.5"-2". A trio would be lovely in your tank. If you are interested in honeys, make sure that you are getting Colisa Chuna, as the thick lipped gourami, Colisa labiosa, is sometimes labeled with the name honey gourami as well. A thick lipped gourami could work in your tank as well, as they grow to about the same size as the pearl gourami.
I'm not a big fan of keeping 3 spot gouramis in tanks under 30 gallons, as they can grow up to 6". They can be aggressive toward other fish in the tank, and they might chase after small fish.