What happened to the original fork? One advantage of steel is that it can be repaired quite easily. Don't give up on your original fork just because it's bent or has trashed threads, it may be repairable.

You need to know the rake of your original fork and the axle to crown distance to keep the geometry the same. The rake is the more important parameter and specifies how far forward the wheel will be relative to the head tube. This will affect how the bike handles so you want to keep it close to the same. You will need a 1" steer tube and the threads need to start far enough down for the adjustable headset cup to be snug against the bearings and long enough for the headset lock nut to screw on. You can add spacers under the lock nut if the fork is a bit too long and you have enough threads for the adjustable cup.

I'd consider getting a threadless fork, too. You will need a new headset and stem but you could sell your old ones and the selection of new forks will be much broader.