Most travel insurance seems to have a 30 day trip limitation, and the only way to cover in excess of this is to take out a "backpacker" type policy for the period of your trip , this will be more expensive.
If you are taking a short haul trip it might even be cheaper to book the cheapest flight home after 29 days, and a return flight out the same day or very soon thereafter . Some people I know would only purchase the "return" flight and say the trip started that day . It would , of course be better for legal reasons, to book, and travel, on both flights.
With a long haul trip the "backpacker" type policy should work out cheaper.