Instead of the mathfont'a italics I would like to try an upright typeface. See for example the P.p on the left of the sample, 1-p in the second \pmatrix and the toprow in the last one.

How can I do this globally, there by avoiding avoiding the need to sprinkle \mathrm's all around as in: \pmatrix{\mathrm  p\cr\mathrm 1-p\cr}. A single \mathrm in front as not enough for the matrices.