1" threadless is fairly rare, most bikes transitioned to 1-1/8" at the same time they went threadless. You can use a shim to adapt 1-1/8" stems to 1" treadless. Unless you already have 1" threadless headset and stem, probably much easier to just get a threaded fork. They have a tiny weight penalty compared to threadless but are much more easily adjusted for bar height.

Measure the existing fork rake and the Axel-to-Crown measurement and try to get something similar to keep geometry unchanged.