We had a tummy sleeper (now he has decided that he prefers his back - why the sudden change, is anyone's guess!!) and used Grobags (and still do). I am not sure of your location or climate, but can tell you what we did/do:

When our boy was your bub's age, we popped him in a 0-6 month 0.5 Grobag with a vest on. This we found was perfect for the warm QLD climate. On evenings when it got too hot, we would pop his a/c on at 25 degrees and switch it off before we went to bed.

In my opinion, the proper Grobags give you real peace of mind because they tell you exactly what bubs should wear depending on their room temperature (they give you a room thermometer with each Grobag). We also had an active tummy sleeper and the Grobag allowed for this. It also helped with the "sticking feet through the cot bars" issue

As for the safe tummy sleeping, my main concern were the loose blankets. I feel much more comfortable knowing that the sleeping bag cannot slip over his head like a blanket could. I think the most important thing for safe tummy sleeping is to not do it until their necks are strong enough so that they can move there head/face away from dribble, spew or any obstruction.