buy a new switch console 
one island has been an animal crossing staple since the very beginning
Ds wii 3ds gamecube.
And on the gamecube you could have multiple islands but that's only because gamecube used memory cards. so one island per memory card
Pretty sure on DS and 3DS you just needed a second copy of the game. Not sure how it worked on Wii.
To my understanding, City Folk functions the same as New Horizons in terms of multiple play files. If two people want their own separate town but only have one Wii, they'll need to purchase a second console. City Folk's save data is stored directly on the system; its data can't be saved to SD cards either.
as I said one island is an animal crossing staple all games work the same.
The only reason why the 3ds and ds releases needed a 2nd game is because the save file was stored on the game cardridge still just one island per game cardridge though all ds games stored their save data on the cart never the system memory. Wii is exactly the same as new horizons as in buy a new console.
still though when you think about it, buying 2 games to get a seperate island is still pretty bad. The only reason why people would excuse the handheld games for this is because a handheld is usually not shared between multiple people. Multiple save files can't be to hard since pretty much all ds games had it.
The most friendly animal crossing games in terms of multiple islands is the gamecube version since a new memory card per player is way cheaper and more convenient, than a new game cardridge or a console.
