I have not fed krill to my gang (all mature now) but they do occasionally get prawns as treats, which I soak in a bowl of warm water for at least half an hour to defrost them and remove as much salt as possible.
You already seem to be giving your little one a varied diet, so don't worry too much about adding to it.
It is a good idea to start a wormery. I haven't done that yet, but I have a very good local store that deals with fish, reptiles and amphibians, and they sell a range of live food, including earthworm, quite cheaply. :happy: