I'm not sure but it's never stopped me from posting before.
Height, weight and ability I believe are the key factors in picking a ski size
. Terrain would be used for ski type
So if you had a ski that was good for you, then lost the weight, you should be able to use the ski since your legs aren't less strong and you should have more energy.
Other things that might come into play are body shape. If your "dunlop" is gone or you no longer are renting out advertising space on your butt, that could change your natural fore/aft position and when you start skiing, you get in your old position. You might need to find your new "svelte" position.
This gets proven every time someone puts on a backpack with some weight in it.
If skiing is all about balance, it could be that you need to work on your balance again. Your muscles knew how to keep the old you in balance and now they have to learn how to keep the new you in balance.
Loose that much weight and your foot is probably slimmer too. Same with your calf. If you're using the same boots from pre weight loss, this will probably be affecting you too. Sloppy fitting boots = poor performance.
Loose enough weight and you might not be packing the weight you had in the past to flex your boots easily.
If I'm wrong, blame Epicski. I'm just applying things I learned here