FWIW, this is what I found worked best and most simply:
Create a blueprint called “BP_SingleMesh” with a single mesh in it. In your blueprint (where you want to spawn a simple mesh into the blueprint), use a SpawnActor with your BP_SingleMesh, then use a “set static mesh” node.
So “SpawnActor(BP_Blueprint)” ===> SetStaticMesh(TheMeshYouWant)
This seems a bit wasteful if you need to spawn many meshes into the scene, but basically it came down to “wrap it in blueprints and spawn normally” for me.