I use this. They fit almost everything so far including biggish gatefolds.

Big Fudge 100x Vinyl Record Outer Sleeves 12" LP | Durable & Wrinkle-Free | Crystal Clear & Made from High-Density Polypropylene | 3 mil Thick, 12.75” x 12.75” | Fits Most Gatefolds and Double LPs https://www.amazon.com/dp/B07816ZPKH/ref=cm_sw_r_cp_api_i_yhZHFb6VT92KD