South Flowing Class I-II rivers in NZ?

I am planning a traverse of New Zealand in a few months, generally following the Te Araroa trail (from Cape Reinga in the North of New Zealand to Bluff in the South). We’re hoping to do some packrafting along the way, and I am struggling to find information. Any suggestions for south flowing rivers that are pretty mellow (mainly class I or II, with portaging options for larger rapids)? Any insight would be helpful! Thanks so much!