So here is my input... As far as springs there a a number of choices and a good dealer will be able to help you out and explain the weight range difference. I know this because when I bought my 2000 Ski-Doo MXZ 700 the first thing I did was put the heaviest springs I could on it. Then when buying my 2015 ZR9000 I did the same thing. In both case there were about 4 spring choices with overlapping weight ranges. In my case the heaviest springs where the same part number listed for Race application and for the full true touring 2-up. I'm a big guy and this is what felt the best to me. Trust me my lighter weight friends said it was like trying to ride sitting on a brick. So getting the correct weight will be key. With that said, I have run an add-on 2up seat for my ZR 9000 (129") with my son since winter of 2019.<br><br>I can tell you for the most part he thinks it is comfortable. But with the 129" track you definably get the back of the school bus feeling on bumps. I would suggest the 137" (When buying mine trailer space was an issue. Not any more.) As far as his hands, they do get cold normally more towards the end of the day. Either way go with something to keep the second riders hands warm. Here are you options:<br><br>Heated hand grips wired to sled.<br><br>Heated gloves (FXR Recon) worked very well but batteries die... 2.5 to 4 hrs. My son liked the hi setting even if he did not need it. Kids grow fast... I just made him use my 3XL gloves but they worked.<br><br>Heated glove liners. Since he was ok wearing my 3XL gloves I invested in some Men's XL FXR Fuel Gloves (Women's sizes work for small kids too)<br>1.) they are great warm glove compared to the junk made for kids.<br>2.) large enough to fit a liner inside the glove with some room.<br>3.) The glove warmth holds the heat in as well.<br>4.) Quick connect once wired to sled and rheostat temp adjustability. <br><br>The two cons with this setup are the wires and dial to adjust the temp can be hard depending on the age of the person using it.<br><br>With that said, I'm thinking of selling my setup this year. The seat would not work for you but if you interested in the glove liners and wires let me know. We have used them on only 3 trips. I bought them in summer of 2019 then had to have back surgery, so no riding for 2020. Then just used them this year. Next year my son will be on his own sled so we won't really need any of the setup anymore. Lastly, the rheostat temp adjust has dual outputs controlled independently. So you could add other heated accessory or even another set of glove liners for your wife. <br><br>One last question how many kids do you have? Another option could be an Equinox 685 Snowcoach. I did this when it was just me taking both of my boys. We went to the 2-up seat once my oldest was on his own sled. <br><br>If you have any questions feel free to ask.