I glue my tulle directly to the bodice, because I like how it's flatter at the top to make a smoother waistline, if that makes sense. I use 2-3 layers of tulle (and I still haven't posted pics of the part you wrap around the waistline
I'll do that in a bit, I did take the pics, now got to get them resized and uploaded. My children tend to ignore me until I am busy doing something then hound me like crazy until I give up and put it off.). I sort of smoosh it onto the glue, and it does soak through. I give it a few seconds to cool off, then use my fingers to press it down really good.
As for the materials for the base, I have been using foam core, I think a lot of others do too, I have seen cardboard mentioned as well, but I like that foam core is light but rigid.
I made my bodice template to fit a 8.5x11 sheet of paper because that's all I had when I made the first one, and it seems to be a good size so I went with that. I just googled leotard and found one I liked, and freehanded the shape, I didn't feel like printing out the picture.
I use 12" strips of tulle but I use the top inch to glue, so my bow holders are probably about 22" altogether. I want to make a smaller one too, haven't decided on a size for it yet though..I know I'd want it to still be full, just smaller, iykwim.
I'm curious what the secret is too!