Apple Watch nickel

Besides the good advice from Rudegar, please also keep in mind that Apple offers a 14 day return policy. That should give you ample time to see if you can comfortably wear the watch.

Side note: I find the Sports Loop bands to be very comfortable. They do not have buckles or any metal and have never caused me any irritation.

Wearing your Apple Watch - Apple Support

This contains information about Nickel content

if you put on one of the rubber watch casings then only part of the watch itself that would touch your skind would be the glass part with the sensors

and bands then if it's not a metal band then it would not contain nickle

otherwise you can ask in a store that sells them if they have some way?