out of ideas for what to build in my survival world

set yourself a goal that forces farms. a full beacon pyramid is a good one, you end up building an iron farm and a gold farm on the way and each of those turns into a build of its own.

Pick something huge and slightly pointless. A road or rail line linking every biome you've found, a wall round your whole area, a full-size replica of somewhere real. Mapping out everything within a few thousand blocks is surprisingly addictive too. Have you got a villager trading hall yet? That one eats weeks.