I use a big square of nylon, as is. No stitching, less to go wrong :) bungee cord around boiler to keep the edges in place, tucked in. Gives malt optimum space during mash. Bungee off after mash, gather corners, dunk sparge like a massive tea bag. My original square lasted nearly 18 months! Not bad for three quid. Eventually it started to get tatty and let excessive matter through, so just bought a new one. Might try getting two, doubling up and stitching the edges... Imagine it might help for a clearer wort.
... Anyway, it's worked for me!