describe a method that would give me the best results to find the thickness of one sheet of notebook paper?

If you have a ream of notebook paper available, you can measure the height of the stack and divide that by the number of sheets in the ream.

Or you can look up the average density of notebook paper, measure the mass of the sheet, then find the volume by dividing its mass by its density. Then divide the volume by the length and width of the sheet.