The main thing is to keep them cool if you can and adding blankets is definitely not a good idea as heat is a bigger contributor to SIDS than sleeping position (and last time I checked the advice on position was heavily based on evidence of correlation rather than causation.)
once your baby is about five months old she will learn to roll over as part of her normal development. By this time the risk of SIDS is lower, and it's safe to let your baby find her own comfortable sleeping position. By then she can turn her face to the side when sleeping on her stomach, which keeps her mouth and nose free.
Personally, both our daughters would only sleep on their tummies - no amount of just letting them cry it out worked as they just got really distressed and any attempt to turn them once they were asleep resulted in them waking up (and being very cross about it) the only exception was in the car (of course!)