For top case security I recommend Phil's replacement plate or the GIVI SR410 support arms for some reason unknown to me the Givi arms no longer fit newer models like yours. I'm not aware of why that would be the case (bad pun intended) as I'm not aware of any frame changes at the rear of the bike?
...again Welcome and best wishes finding arm rests for your boy.
Welcome to the forums, and congrats on the Connie! I have a 2015 Connie and I learned the hard way that the Givi SR410 would not work with 2015's -- there's evidently a tab on the rear frame that prevents it from working. I returned the Givi and went with the Phil's Farkels mounting plate myself -- Phil was very helpful when we were sorting out why the Givi wouldn't work.
Using Phil's mounting plate with the Monokey tab, I have a Givi Maxia v56 on mine with a back pad -- My son likes to ride with me also (he was 12 when I got the Connie). I also added the Admore Lighting to the topcase, and I'm very pleased with that.