Welcome to BYC. If you put your general location into your profile, people can give better-targeted advice when climate matters.
Anything that cushions the hard bottom of the nest can work. Shavings and straw are the most popular but there are also a lot of people who use hay, hand-harvested long grass from their yards, and commercially-made nest pads among other things (I personally don't like shredded paper because it sticks to the bloom on the eggs, but some people use it).
Use whatever is locally available at a reasonable price.
Then expect your Point-of-Lay pullets to kick it all out of the nest as they explore and attempt to figure out what their strange hormones and instincts are telling them.

It's not that they don't like the material, it's just that they're teenagers who don't understand what's happening to them.
Make sure that you've got a good lip on the boxes and refill them as needed.
In re: curtains,
I'm in the "just something else to clean" camp, but many people like them so put them in if you want to or don't bother if you don't want to. The chickens will be happy with any nest boxes that seem cozy, secure, and safe -- and they're a lot less fussy than the humans are.
P.S. in re: nest eggs,
I like golf balls for nest eggs because I can tell them from real eggs by touch when reaching under a broody. Anything roundish and about egg-sized will do from fancy realistic ceramic eggs to kinda-egg-like rocks.