As you learn more about ultralight packing, you'll also discover that you can use your sleeping pad to form the frame of your pack, which lets you use a lighter pack (and there are some patterns out there that let you sew your own pack, since you don't need a preformed plastic/metal frame to build it on.)
I've heard of that. In fact that's my tentative plan for getting a decent pack, with a bit of a twist. I found good notes online about building a tarp out of silvered LDPE and using strategically placed "transparent duct tape" to carry the loads. At least one experienced camper has built several of these and used them for years, and I thought if it works for a tarp, why not a pack, except I wouldn't need the heat reflective stuff for a pack. Is there any particular pattern you would recommend as a good starting place?