The risk of SIDS drastically decreases after 12 months.
Go buy the Angel Care Deluxe Movement Monitor.. it sounds off if there is no movement detected for x seconds (we had a few false alarms once my son learned to stand up, BUT, we learned to turn it on after we knew he was asleep, and no more false alarms)... now, it seconds as an escape alarm for whenever my son finally figures out how to climb out of the crib :)
I'd gladly pay 3x what I did for that monitor!!
When my second child was about 2 1/2 months old, I was babysitting a 5 week old baby as well. He passed away from SIDS, in my care. I didn't know about the movement monitor, and life was hell after that, I was so upset about the loss of this child, and scared for my baby's safety. I didn't sleep for MONTHS (literally... I would lay awake and make sure she was breathing).
When I was pregnant with my 3rd, I told everyone he was NOT coming home from the hospital until we had that monitor installed. The peace of mind if PRICELESS.
BTW, my first daughter favored sleeping on her stomach... she was fine. Since the passing of the baby (baby Dylan), they've found an actual genetic link in babies who die of SIDS. Unless your child is prone to sleep apnea spells, start breathing easy!! The fear never completely goes away, but it does get better over time :)
AND, at 11 months, your child knows to move if they can't breathe, like if the blanket smooches against his little face. A blanket is not only fine, but probably necessary!! :)
LADIES, I'm reading a lot of off information on here. Babies should be placed on their backs to sleep, hence the 'back to sleep' campaign against SIDS. Here's the thing: once a child can flip themselves over, you do NOT have to wake them and flip them on their backs every time, no one would ever sleep!
Blankets, pillows, stuffed animals, etc are mostly dangers to newborn's who do not have the neck muscle control to move themselves if something covered their faces.
Kids don't like to be smothered. They're going to fight like hell to breathe. A 5-6 month old has the neck control to move if they can't breathe... an 11 month old most certainly can. I'm not saying put a huge, queen size comforter in the crib, but a light blanket is perfectly appropriate.