I've got to think that the 'baby' yarns are thin for a reason.
When my son was a young baby my favorite blankets were flimsy knit ones. I loved thin and drapey fabrics because they seemed so much softer and cooler on warm days. They were also easier and more practical to swaddle him in as a newborn. 'Sturdy' didn't matter to me as much as weight and softness. I will say that I set aside the really holey blankets because it drove me nuts when his little fingers and toesies would peek through.
I think the DK weight yarn of the Bernat Softee Baby (which is SO soft, I love it!) would be fine single stranded as long as you don't mind a lighter blanket. If, however, you want a thicker, warmer blanket you may want to look into chunkier yarn or different patterns.