Hi Clare and welcome to Lombok Lovers
I am afraid there is no map on the forum but you should be able to find one easily enough on Google.
As in Bali, the airport in Mataram has a prepaid taxi booth. As you are leaving the arrivals it is the last desk on your right hand side. I am not sure what the current taxi rate is it is usually a little less than the price of a car charter which is currently Rp250,000 to Kuta. The journey time is about 75minutes.