[QUOTE=What would be a good mob to train on that doesn't hit too hard?[/QUOTE]
You might try the centaurs in South Karana. Centaur Chargers are level 29/30, which should be perfect low blues at level 39. There's even a Centaur merchant nearby, who'll buy all the stuff you loot off of his dead compatriots.
As others have said, there are no shortage of mid level creatures to find and fight in the game. Browse through the
Per-Level Hunting Guide if you need more ideas on where to start. You might avoid giant things like hill giants and cyclopes and such though, as I believe that they have an innate damage bonus compared to other creatures of a similar level, so they'll hit harder than they otherwise should.