When I made mine, I just took 2 terry washcloths, folded them into thirds and stitched the two short ends. That's it and they work fine. A few years before I made those, I did take the time to cut flannel and contour the sides and stitch them and add snaps to wings and all that, but the terry ones I made work just as well. Actually, the terry ones i like better because they dry faster. As long as your underwear isn't loose, it should work fine.
I have been thinking of adding a layer of PUL to some of them for when I go out, but i typically use my diva cup when out, so I haven't gotten around to it.