From the title of your post, is your concern that the floor heating element+insulation will overly elevate your floor? It is my understanding that insulation is only recommended when installing over concrete/slab (like my BR) as it tends to suck heat. But there is even debate whether that's at all necessary. But is doesn't sound like you need it over wood.
I decided to put down this. I got it @ $18 for 8 square feet, free shipping.
http://www.cerazorb.com/