Andy, next time you are in the big grocery store or a natural foods store, buy a pound bag of yeast. It keeps forever in the freezer (at least a year) and a bag will cost you about the same as a couple strips of packets.
I find that exact measurements of yeast are not too important, and if I was using packets for your recipe, I would use one. Maybe mix it with water and a bit of flour and sugar and let it grow for an hour on the counter before you mix up your dough, just to increase it a bit.
I just haven't been the same
since that house fell on my sister.