Doing some research into possible causes for more pressure on one sit bone more than the other (left side in my case), it is suggested to go get a professional fitting.
While I'd love to do that, I'm just a poor retired GI and simply can't afford it.
Any suggestions on what I can do on my own to get some relief?
If you have a difference in leg length, sometimes it's recommended to set saddle height for the longer leg and shim up the pedal or shoe on the shorter. Another idea (from the Selle Anatomica fitting guidelines) is to rotate the saddle so the nose goes toward the side with the excess pressure. If you do this, just move the nose 1/16" at a time. And keep the saddle height exactly the same as before the adjustment.
Retired GI (I'm not)? you're probably about my age. PM if you'd like to talk some more.