Finally bit the bullet and installed mods, I've been playing survival legit but I just couldn't see myself paying 2000 caps for a partially functional house. So of course I went far past the nessicary mods which add full workshop functionality to home plate, and link the internal workshop with the others around diamond city.
I've now installed, true storms, darker nights, scrap everything, build everywhere, 2 mods for diamond city radio, extra settlement building stuff, improved map, and then because bathesda thinks mods are cheating I've also been forced to install F4se to patch back in achievements and the command console.
Then I ran a few commands in the console, player.placeatme c1aeb to spawn a workbench in the city, then setlocationcleared 00002cef 1 to make the bench unlocked.
Now I can finally build a chair in my upstairs room overlooking the city. And yes technically now I can scrap and build all over diamond city but I'll try not to abuse the power. It's just not immersive.
However, aparrently things I build outside may vanish when the cell updates, I believe there is a console command to fix this.
I experienced a bug with scrap everything, I couldn't sprint near the edges of settlements, there's a patch for fallout4.ini the nexus mods page for that mod.