Channa Bleheri 6" - Small group, can play with others
Channa Assam 5" - Small group, can play with others
Channa Gachua (Depending on varient) 6"-10"
There are loads of slightly larger single Snakeheads you could keep.
Channa Stewarti is a good example. 10"
All of these will eat any fish they can swallow, usually between a third and sometimes half their lenght.
Where abouts are you. I know Wildwoods, Enfield, London have just had a good delivery this week. I have my eye on a couple of them.