+1 Don't get the kids board. As you ride mostly groomers, get the 144.
+1 Consider if you want Camber or Flying V. When looking at the Feelgood you have to be aware that the ADULT board is offered in both versions. You need to the get one that is right for you.
If you want an easy, breezy, catch free ride, then the Flying V is the way to go. It has a playful, loose ride and is great fun on softer snow. ( not much edge hold on hard pack ) My daughter is about your age and rides a 2012 Feelgood Flying V and loves it when the conditions are soft. She is not so enamoured with it when things get hard, frozen and icy. Way too much drift and slip.
You mention that you have knee issues and the Camber version is a lot more likely to hook an edge and put you down and your knees won't likely take too kindly to hard falls.
Do a lot of reading on the boards here as there is some great advice to be gleaned if you take the time.