Narrow or comfort saddle?
You should ride whatever you find comfortable.  If the old saddle was good, swap it to the new bike.
If you intend on riding both bikes, keep eyes open for a second saddle of the same brand/model.  You can store or sell the original saddle.
Saddles are a personal thing, noone can tell you what will be comfortable.  Since you call the narrow saddle comfortable, go with it.
And if you don't like it on the ebike, swap back with no harm done.