Is there a buffer I can take with it or another pill less painful?

"Morphine will also cause constipation. Drink plenty of water (six to
eight full glasses a day) to lessen this side effect. Increasing the
amount of fiber in your diet can also help to alleviate constipation."

From: http://www.drugs.com/morphine.html

Take it with food.

If that doesn't help, there are several numbing agents that could be
used alongside it. Prochlorperazine, chlorpromazine come to mind.

Oh, I certainly take it with food, or at least milk, and it does
fairly well for the pain for which it is intended, but often gives me
a stomach ache or hearburn for an hour or more. I just wondered if
taking it with, say, baking soda & water or "Tums" type antacid would
compromise its action.
As an aside, the stool hardening is welcome because my other meds have
the opposite effect!