On my mill I used a pair of ordinary angular contact bearings and sprung them using the end of an old square section air rifle spring crushed close to solid.

It's all rolling contact so it spins freely on the handle, the spring compensates for temperature change and it doesn't move one jot unless I make a horrible mistake.

If your frame can take the strain, one bearing at either end is definately best because it keeps the whole thing in tension. I used two at one end but plan to rework it with die springs when I get the time because it works so well and I have become anal about the .003" backlash. I'm thinking 2 ball nuts and another spring.

The cheapest place I found for the bearings was VXB Bearings on eBay, cheapest despite the trans-pond shipping.