Go countryside, they said, it'll be quiet.

Except for: tractors, harvesters, mopeds, quadbikes, chainsaws, circular saws, nailguns, lawnmowers, leafblowers, snowblowers, diesel generators, motorboats, skijets, snowmobiles.

This.

I moved to a countryside 2 years ago, escaping from city noise. Now, I’m going back (although to the outer, more quiet side of the city) because I’m going mad - lawnmowers, dogs, tractors, diesel generators, dogs, dogs, lawnmowers, dogs, …

Already exists, same as is used for any other soundproofing. Rockwool insulation, resilient channels and a second layer of drywall, mass loaded vinyl, acoustic panels and tapestries (can hide some more mass loaded vinyl in there too), acoustic adhesive, scored screws to kill floor squeaks. They're all quite expensive but hey! Very DIY accessible.

For exterior noise the biggest bang for the buck is replacing windows. I had some soundproof windows put onto my previous house and you could close the door on a parade going by and not even know it was happening.

Curtains add a flexibility to the use of space that walls do not. If I only have overnight guests very occasionally, I don't want to wall in part of my living room to accommodate them, but I'd love to be able to hang a curtain from some removable hooks that would give them some real noise privacy.

Tell your family to stop motorbiking to the bathroom in the middle of the night. Bam, problem solved.