As ishaw says, any 8 or 9 speed Shimano shifter will work fine with your M960 rear mech in terms of the cable pull. But the M960 is Rapid Rise (reverse action spring), designed for use with the dual control shifters. There were M960 and M970 dual control shifters, and there was a Deore, LX and XT model too - there were different models for cable brakes and disc brakes too. There was no M960 trigger shifter specifically since Shimano - mistakenly put all their eggs in the dual control basket for the M960 series. However all the other 8 or 9 speed Shimano trigger shifters will still work with it (even road shifters for that matter!)
But - since the derailleur has a reverse spring designed the make the shifting direction more intuitive with the dual control levers, if you use a normal trigger shifter each click will move the rear mech the opposite way from what you're used to, so a thumb press will shift the chain down the cassette from a larger to a smaller sprocket, a finger click will move it up the cassette into a larger sprocket.