Farming Flora Frostbite is an easy way to get level 4 Decorations (Takes about 2 minutes depending on build) : r/MonsterHunterWorld
PSA: If, for any reason, you're using decorations that you don't have 4 slot versions of (bow charge up, guard up, capacity boost, est) the fatalis waist alpha is 100% better then
Monster Hunter World Iceborne Skills, Charms, Mantle, And Decorations. Here's All You Need To Know