Margie, I think that would be beautiful ! I wouldn't think that it would block heat, just become part of the mass, but maybe some of our local experts will chime in on that.
If you do it I would love to see some pictures !
The one caveat might be that glass or tile mosaic surfaces might be more conductive than cob/plaster and feel hotter when sitting on them. This *might* be a drawback, if the mass gets to the high end of the comfort scale, though it could probably be ameliorated by a drape to keep skin from direct tile contact if it is hot.