I downloaded that babybedding app and spent the time to make a bedding that I liked and when I went to purchase it it was $300... Just to let you know, it's pricy haha
It's not a website, but resale shops are awesome for baby stuff!
I just found a website for baby bedding. They have a lot of different things to choose from. You can even design your own and then you can match all the decor with it. It's really cool :) www.babybedding.com