When I PP, I use a 1.5 stitch length. I use Carol Doak's paper for PPing, and it works great. It's sort of like newsprint, cut to fit your printer. If you can find a source for cheap newsprint that will fit in your printer, that would be my choice. I never have a problem with stitches unraveling when I tear off the paper.
The suggestion for the vellum was the cheapest I've seen it anywhere...that's actually cheaper than you can buy Carol Doak's paper at retail.
LOVE your heart block! It's gorgeous. Have fun paper-piecing...you're now officially addicted! :-)