2001 Honda Civic Automatic Transmission

Car would not go any further. Parked it on the side of the road. Checked the transmission oil and it was ok.Next day, started the car and tried to drive it. It would drive but hesitate in "D" but would dive fine in "D2". Drove it towards home in "D2". After 15 minutes, would not go any further, just like the day before. I got it towed to home. Mechanic thinks the torque converter is gone and will replace the transmission and the torque converter. Could I just replace the torque converter (new) or change the whole thing (used)?

Thanks