It's easy anyway, you write out your will, dated, signed all that.
You have 2 people who don't benefit from the will also sign it, dated, details etc.
Then make copies and give to spouse, executor, whoever.
Just to add, both witnesses have to sign the will at the the same time, i.e. each one has to be present at the time of the other signing.
I know several legal exec's who will do your will for free, after all they are the ones who have to administrator the will for the lawyer ( they do all the grunt work and the lawyer gets all the glory )
There is a lot of sensible information. i.e. Give a copy to executives of the will, use someone you know well and trust to be the executive.
While I have had no experience with public trust directly, a former colleague of mine father passed away suddenly and his will was with public trust, there was not alot of money but they ties it up in court for several months and bled the estate virtually dry.
Also the person you elect is allowed to charge the estate for their time while sorting things out.
The other thing you might like to do at the same time is sort out power of attorney, there are two types in NZ ( financial and medical ) and you can remove them at any time.
While you can do it yourself, make a visit to see your family lawyer or their legal exec.
Congratulations on being a grown up - sucks some times to have adult conversations but you need to from time to time :-)