I bought some poly that is made by Warm & Natural called Soft & Bright. It's the nicest batting I've worked with. There's no shredding or bearding, no thin spots, doesn't pull apart easily and the loft is just right for me. It lays flat and doesn't curl up. I get it at Joanne's with a coupon; comes on a bolt for I think $7.95/very wide yard. I don't use cotton because it seems to pull apart too easily. This one washes up beautifully-use it in kids quilts all the time.
Regarding the melting of poly, any fabric will cling to skin when burning. If you look at mattress pads, crib pads, etc., most have some poly in them. Wish there was a 100% safe fabric but so far I don't think it exists.