To bring a chisel, plane iron or knife to the ultimate razors edge, you need a buffing wheel. There are hard felt wheels available at many woodworking suppliers, but these are costly. If you have some scraps of MDF, you can make your own.
I made a short video about it:

For this example, I put it on my lathe, but it can easily be made to fit on a bench grinder or mandrel. You will want to arrange whatever you are using so that the disk is turning away from you.
The great thing about this is that you can shape the disk any way you need: half round for the inside curve of a gouge, for example.
Also, as shown in the video, a straight strip of it is great to strop knives on.