There is a list of 'base structures' on the wiki that prevent spawns within a certain radius. Among the various items, non crafting ones you might place without being e;ye jarring would include portals, all the various torches, bonfires, campfires, and possibly some others.

Just use a workbench selected in your build menu to determine the radius of the suppression and then put down whatever you want at the location you determine. You can even use workbenches just temporarily to help you determine suppression coverage - then after everything is covered and arranged as you like, replace the workbenches with torches, portals, fires, etc.

The torches especially are easy to hide in other structures if desired and I believe they are like campfires in that they don't need to be lit to still suppress.