I bought some disposable Dixie Insulair® hot cups last night. But cool insulation-themed name aside, they didn't feel insulated (read: blazing hot) with coffee inside. So, I began digging around in the cupboards for a cup cozy or some other cup I could use.
I spied these fire-engine-red Chinet cups, which I picked up a Costco some time back. I put my hot cup of coffee inside. It worked! The ridged walls help to insulate and keep my hands cool. All it needed was a better fit, which was easily accomplished by cutting off the base of the cup.
Any similar cup should probably work, too. Experiment with any large plastic cup that has some sort of texture or ridges in the walls and see what works best.