There are others who will have more sage advice than I on specific saddles and issues but...

I get more pain in my sit bones in an upright position than in a road position, so I wonder if you're really letting it rest and heal (not that that's the 100% solution for sit bone pain). Would the saddle on the mixte work on your other bike? Maybe try that one since it isn't causing you pain? I'm sorry - that sounds very frustrating!