I found one of those corded plug-in dimmers at a thrift store and use it in our spare bedroom. It has an always-lit neon night light under the slit for the slider switch for easy location in the dark.
The other option would be an in-line switch. A plain one, or one that has a two-position high/low dimmer, or the more bulky rheostat type that have a flat rotating thumb wheel for full range dimming.
There are also modern sockets with infinite control switches for dimming. A pair of our living room lamps have them, and I've seen tented floor lamps for reading that also used them. It may be possible to retrofit your lamp using a socket of that type.