You must provide more details or you will not likely receive any useful help. This is much too broad a subject and we cannot help you without knowing the application. I have a question for you:

I want to design a shaft. I need it to be about 3 feet long. What material should I make it out of?

If you answer my question, I will answer yours.

Johnny Pellin

I think an Eng-tips member has a tag line that includes this wonderful Sherlock HOlmes quote -
“It is a capital mistake to theorize before one has data."
"IDENTIFYING THE PROBLEM
Evaluating the needs or identifying the problem is a very important step in finding a solution. An
improper definition of the problem will cause the engineer to waste time or arrive at an incorrect
solution. "
http://webpages.uncc.edu/~jmconrad/hsed/intr_0in.p...

I'd base my decision, in part, on the housing dimensions and COTS (commercial off the shelf ) bushings.
I'd choose a material on rpm and lubrication conditions and expected life. There // may // be a hybrid metallic material (Teflon filled bronze, etc) that would yield good life in marginal lubrication conditions.

There is a kg ( 2.2 pounds) of basic useful bushing/bearing design material in typical machine design text books.
Stuff like acceptable unit loads for different bearing materials (which will help arrive at an adequate bearing length, shaft design (strength, deflection, critical speeds, machinability for including driving/driven features and a LOT more).