Hi Debbie. I can provide some general guidance, but I recommend you talk to a lawyer who can give you some legal advice where that advice can be based on the specific nature of the product.

Generally, it is relatively easy to protect the expression of an idea, it is comparatively harder to protect the idea itself.

If you are commissioning a student to develop the product, then any technical specifications, design files, or code (if there is software) will be protected by copyright automatically and you (as the person who commissioned the work) will by default be the owner of that IP. However, it is advisable that you make the ownership of those work products very clear in the contracting or employment agreements with that person.

However, the ‘gist’ or the ‘idea’ of the product could be copied so long as they aren’t copying any of those specs, design files, code, etc etc. This is where patent protection comes in. But patents are a comparatively longer and more expensive process and I recommend experts to help here.
You mention the product is ‘not available in NZ’, which made me think this product may already exist overseas? If so, you may not be able to patent your invention because it is not novel. Ie, it already exists elsewhere.

Many people suggest that the fastest way to ‘protect’ your idea is just do a really swift and good job of going to market so that you capture the market before anyone else. That is another thing to consider.

Good luck!