Yeh MOFI sleeves have been my go to for a while. I used to get poly sleeves from sleevetown (now sleevecity) but their s&h made that unreasonable for me. They were quality sleeves though. I picked up some sleeves from third parties on Amazon but quality control was generally poor. They worked OK, but I'd end up tossing one in every five when the seams split. I guess it was still cheaper than MOFIs, but tossing out new things generally makes me unhappy.
Plain paper's fine for my less cherished LPs. It does break down over time (like 20 years). I haven't had a poly sleeve do what the OP showed (yet).