Improving Harry's quality of life
keep food secretly, he's even got a moleskin no one else can touch, he's seen a tent with an entire flat in it....there's legit no reason for him to be that accepting
Space expansion charms - Take a tiny shack? make a mansion. A nice size cottage? an even bigger mansion. A small plot of land in the middle of the ocean? A massive island (build Atlantis [Bubblehead charms, gillyweed, transfiguration.])
take a trunk with a home inside it, slap it with muggle repelling charms, and then put the trunk in the shed. He's still physically there, but yanno, not abused
teaching him illegal apparition
Bribe the Dursley’s or threaten them and use consequences if they mess up (ideally Sirius or someone polyjuiced to look like him since they already fear him)
Buy Grunning’s and threaten Vernon with his job
Take Harry to regular medical exams to check on him
Give Harry a safe and fast way to escape should anything happen (the wards clearly don’t protect him away from the house, so what is he supposed to do if some DEs are hanging around?)
Get Mrs. Figg to actually do something instead of smelling of cabbage and getting hit by cars
have Bill enchant something like a protection or notice-me-not amulet