I would highly recommend not trying a backflip on skis if you are still sketchin on a tramp. Just keep on going for them on a trampoline until you feel totally relaxed doing them. A good way to make progress towards being able to do them on skis is to try to do 2 or 3 backflips in a row on the tramp. That way when you come down from your first flip you will know for sure that your landing square and stable. Additionally, this wil be a great intermittent step seeing as throwing 1 backflip on skeeze will be waay scarier than doing a few in a row on the tramp.
Remember, baby steps....