Wool batting is warmest, but it's important to use only reliable brands such as Hobbs or Quilter's Dream. These wool batts have been treated to reduce shrinkage and fiber migration (bearding). Wool "breathes", so it is also relatively cool in summer.
Silk batting offers a lot of warmth with the least amount of weight, and it is also cool in summer. Silk batting is very expensive, though. It is often used in quilted clothing because it does not add a lot of bulk.
Why do you love the idea of using 100% bamboo batting? Is it for environmental reasons? Because you really need to understand how the bamboo you use is processed if you are looking for something environmentally friendly. This article is a start:
http://www.seamstobeyouandme.com/201...amboo-batting/
Why exactly do you want a thick finish? Is it because you think that quilts should be thick, like the modern comforters you can buy in a store? Vintage quilts are much flatter than that. If you like a high loft batting, then be aware that they are more difficult to quilt -- both by machine and by hand. Most quilters use medium loft or low loft battings.
Flammability has little to do with the cost of batting. Quilts in general are not a flammability hazard for children because they are thick, which means that the amount of air available to feed a fire is limited, which means that there is time to move the quilt away from the child. A single layer of cotton fabric -- think draperies, or a nightgown made out of untreated cotton flannel -- is dangerous because air surrounds both sides of the fabric. Touch a flame to the bottom of a single layer of fabric and the fire will explode upwards -- engulging a child's head in flames before an adult can take action. Quilts do not have this issue. An all-cotton quilt will tend to smolder and burn very slowly (or even extinguish itself) because it is thick.
I don't know of any single website that explains all of the differences in battings. There is a lot of information on the net, though. Try Googling the manufacturer brands you are interested in, as the good ones provide quite a bit of information about each type of batting they offer -- including thickness, distance needed between quilting lines, etc.
Edit: I agree that Hobbs 80/20 is a good batting to start with. And I like Hobbs PolyDown for quilts that I want to be fluffier and lighter in weight -- especially good for children's quilts that will get washed frequently, because the Hobbs PolyDown dries quickly.