Tetris Heart Blanket

I'm in the planning stages of making a baby blanket.  It's going to be based on the famous Tetris heart cross stitch which looks like this:

Except I'm going to make it be one complete heart to snuggle up my baby in.  I'm choosing girly colors like pastel pink and lavender.  I need to take a field trip to Montgomery to look at yarn to pick out the best colors.  I'm using Caron Simply Soft as its inexpensive and 100% acrylic, which means it's machine washable and I believe is better for sensitive skin. I worry that since babies can't have honey or many other foods because of potential of allergies, it's best not to use animal fibers. Most baby yarns are expensive and consist of chenille or cotton, or even bamboo silk yarn.  Which is fine, just that cotton and bamboo don't stretch.  I want this blanket to be stretchy and snuggly.  Each pixel of the tetris pieces is going to be made of granny squares. I've been experimenting with square sizes and should have one picked out by tomorrow.