Bunnings is your friend, see Mudski's early posts.
I used the same 'push to open' one as him, but added a couple of small thin neodymium magnets (eBay) to the latch plate on the door, as I found the magnet not quite strong enough & the door sometimes opened on our corrugated road. It helped that I had mounted the latch so it was adjustable, allowed me to accommodate the extra thickness of the neodymiums without pushing the door out. Mudski may not have that problem as he mounted his latch plate on the door differently to me.