I think you are wise to avoid chenille especially for a baby blanket as, in my experience, chenille, even if said to washable, can shred in the washing machine.
I haven't made a lot of things in superchunky but have liked Rowan Big Wool and Wool and the Gang's Crazy Sexy Wool.
King Cole and Sirdar both do a wool/acrylic mix which I haven't tried. You can't go far wrong with the Stylecraft Special range. They do an XL super chunky although there doesn't appear to be white in the colour range only cream.
If the pattern is easy to adapt, I might be inclined to drop to chunky. The Cascade Superwash wools are lovely to work with. Stylecraft Special Chunky is also good to knit with washes well and and is very economical.
Do you use Wool Warehouse? Great range of yarns and excellent customer service.