The cheapest and most convenient solution is just to buy a WM blue pad and cut it down as needed. It won't be the lightest option or the warmest for the weight or thickness, but it's all I have ever used so far. This is all I have used for years now, going along on on all my trips. For the legs with my "Yeti", or placed into the pad pocket of my JRB bridge, or even placed under the hammock inside of a Speer Pea Pod. But mostly just used for sitting around the camp fire or for lunch breaks when the ground is cold and wet.
But if I was really counting the ounces, I would go to the trouble of getting something lighter.