i'll link the tool for viewing seeds i used.
https://github.com/toolbox4minecraft/amidst


EDIT.
found i can upload to imgur with an account.
removed the text regarding it....
edit over.


the island has NO villages.
no buildings of any sort.
so you can build a big city there.


the seed is a dumb one...

pewp
OR
3437454


set the world to large biomes.

you WILL spawn in the ocean a quite far away...

i reccomend you use a teleport command.

either enable cheats for singleplayer or open to lan and enable cheats

go in creative, because if you sink and teleport, you'll end up inside blocks and die.
fly upward a bit.

then type in

/tp @s -536 ~ -696

that will take you to the forest island.