I had no idea what to say. You're going to have a looser, softer, lighter look. And, they definitely will cost more. Also, you will approach them differently as an upholsterer, because you're going to cut them different than you would if it's merely wrapped foam.
Some people are allergic to feathers, and opt for kapok or puffball dacron.
You can get the high crown 'look' of feathers using foam and dacron, but not necessarily the feel. You simply layer on bonded or quilted dacron starting out with smaller pieces and building up to pieces the size of the foam, til you have a soft, rounded look, similar to a down-filled ticking cushion. There are so many combinations of seat and back cushioning to choose from. I'm sure others on this board have some insight and ideas to help you out, too. If I think of anything I missed, I will post again.