Mob Stay Longer Mod increases the mob despawn distance in Minecraft Bedrock (like 100 or 200 blocks), stays compatible with achievements, and doesn’t need Experimental Features, but you’ll want to watch for lag and bigger world size.
Snow Temple Mod adds a massive Snow Temple structure packed with Strays, Zombie Villagers, trial spawners, vaults, secrets, and a projectile-only boss called The Frozen King.