The batting makes a huge difference in softness. Although you mention 100% polyester 8 oz, what is the brand? There are good brands and not-so-good brands of batting. In terms of a polyester batting, I believe Quilter's Dream polydown is supposed to be one of the very best. (I haven't used the QD yet.)
If you want to make the whales puff out a little, what you can do is trace the whale outline with a Sharpie permanent marker onto paper. Pin this to a spare piece of batting and cut out inside the traced lines. Use a little basting spray or Elmer's washable white school glue to secure the extra batting piece to the wrong side of the top. (If using the glue, you will want to iron to dry out the glue and keep everything stuck together.) When you quilt around the whale shapes, they will puff out a little more than the background. You might want to hand stitch some of the details of the whales, inside the trapunto (or machine outline if you are comfortable with doing that).
I think the bargello side will look fine.
Instead of meandering all of the background, you might want to consider quilting wavy lines through the water (or straight lines following the rays of light in the water) and outline quilting the rocks and mountains. Maybe swirls for the sky and clouds.
Edit: Also, what kind of thread will you be using? Using a finer thread would allow you to do more quilting without adding stiffness. I have found that Aurifil 50wt 2-ply is very good for this. A variegated blue for the top could work very well.
Last edited by Prism99; 10-23-2012 at 11:06 AM.