I have a 2020 with 19K miles and the wife has been 2-up for about 2/3 of that. We ride together at least once a week sometimes twice a week. She likes the jockey position of a sport type bike as opposed to a tourer or cruiser, she refers to herself as the backpack! When we are in cruise mode she will sit up a little, but mostly she is close to my back and relaxed. She is 5'2" and 120# with little girl feet, I'm 5'7" and 135# wearing a size 8 boot. I rate the bike as plenty big for small people like ourselves. If we both were larger I doubt it would be big enough. I ride on the pegs with the pegs centered between my toe and ball. She rides with the peg centered on your ball. If she stretches a bit and hooks the peg in front of her boot heel, her toes are against my heel. If you guys are of larger stature you may want to test ride any year N1K, they are all the same frame size.
Also, the bike is made for sport touring meaning it likes roads the bend left, right and up, down. It's not made for long stretches of highway or interstate. It can do it, but I would need more breaks if I was going to put on 600-700 miles a day on mostly highway type roads. When we are in the twisties and sport riding, I move a lot side to side and she moves with me, so our bodies get to move around a bit and not stove up from long periods of sitting static. The more often you guys ride the easier and more comfortable you will be as your body does acclimate somewhat. So, what you are used to previously will impact your N1K experience. Previously my wife had about 50K miles on the back of our ZX14's and she loved it. Initially on N1K she was a little disappointed and had to adjust to a bit more of a situp position. It didn't take that long to adjust, but if she was used to the back of something like a Wing, I doubt she would have transitioned well to the N1K. Also, she hates anything like a Wing back seat with arm rest and seat back. She feels closed in and wants to be closer to the pilot and also wants to feel she has plenty of room to bail off during a low or high side. When we mount I let her on first, she uses the rider pegs and grips to get on, then pushes back on the pillion seat and pegs. Then I get on. We reverse that on the dismount. Makes it a bit easier to get around the hard bags as neither of us have enough height or leg length to throw a leg over without us looking like we are doing a high kick!!
I know it is hard to find a dealer or private seller that will demo an N1K and especially 2-up, but Kawasaki will if they are coming to a town near you on one of there demo tours. Hope this helps and doesn't discourage you. I think the N1K is the second best I have owned out of over 50, but it's not for everyone, so let the truth be known.