If you're set on a Pellon product as the Timtex substitute, that would be the Peltex 70, 71, 72 (the only difference is in how many fusible sides it has) that you've already tried. It was most likely the density, not the thickness, that stressed out your machines.
Fast2Fuse is an option no one has mentioned yet. I love it, as does my Bernina. It comes in three weights, all are double sided fusible. The main disadvantage is it's price. I use Fast2Fuse for journal and legal pad covers and Décor Bond for boxes. I don't make bags, so can't give you experiential advice on either brand for that use.
However, here are some comparisons that may help you out.
http://nicolemdesign.blogspot.com/20...nd-pellon.html
http://nicolemdesign.blogspot.com/20...onderings.html