Fofine, this cruxio feller pretty much has it spot on with all the variables.

You really don't want to order a fork on your own, especially if you are not familiar with all the details.

Even if you visit some bike stores for professional opinions, I'd read up on fork and headset info as much as you can to understand the terms.

Also, depending on your bike, it might not even be worth it if your bike is a road bike not suitable for carrying stuff, including maybe gearing not great also.

Really, too many unknowns here.
Good luck