I'm going to be travelling round the south island from mid march to mid april and the north island from mid to late april. I was considering camping as a cheap option but was wondering what the weather would be like around these times. Is it worth getting a really warm sleeping bag or would a normal one be ok?
It depends how you feel cold. My girlfriend needs a 3-season bag in summer, but the same one was toasty for me in Nepal in November!
NZ is much like the UK climate-wise, so judge it that way - if you'd need one here, you'll need one there.
Alternatively, most NZ campsites have small cabins to rent - basically just a garden shed with bunk beds in it, from about $10 a night. This could be a warmer alternative. If there is more than one of you, there are larger cabins too.
Basic ones have just beds, but you can get ones with or without kettle, toilet etc.
Check out www.top10.co.nz and have a look
i was also planning on going to new Zealand in that exact period but heard that as of april the weather starts to get substantially cooler and the treks start closing. from the research my sis did the daytime weather is around 10-15 degrees celsius which kinda got us to cave in and decide to go in feb/march instead. but then, we are Israeli ladies used to the hot and humid weather so for a brit like you it might be alright. generally from what i know you should be fine, but for your knowledge in new zealand on the treks you can get a kind of seasonal pass to stay in huts all over the place and thats pretty cheap. you'll still be needing a sleeping bag though, i dont know what you had in mind by normal sleeping bag cos hey ive got a sleeping bag too and if i took it with me id probably freeze to death, literally. you really have to look into the proper sleeping bags and learn more about what features you need, for ex: a zipper that doesnt open all the way down to the legs so as to preserve the heat in your feet, also take notice of the degrees the sleeping bag is designated for (for example. 0 degrees, -5, -7 celsius) and then check the night temperatures at that time. this is an estimate but i would say you need at least the -5 if not the -7 for when youre going. also there is a design of sleeping bag known as the mummy shape which means thin at the feet, for heat preservation, then widens out. the bag should be hollow fiber which ive heard is good for the warmth and you should probably try and get a sleeping bag which has a drawstring at the head part so you can keep your head warm that way at night. these are all things you should look into from the research ive done. also, try asking about brands such as deuters, north face, ferrino cos i know all three are good.
hope that helps.....