Hi there,
I completly sympathise. I know what its like to be a tummy sleeper and pregnant... Gosh the first night after our princess was born wasnt the best night sleep but just to be able to lay on my tummy agian was bliss...

I used 2 curved pillows in like a square so my tummy was inside the square and i was actually laying on the pillows and not squishing my tummy as much... when we sot further along i would use them lay on my tummy but have 1 legbent to the side so i wasnt fully on my tummy... its hard to explain.

I suggest lots of pillow until you find what works. As for the ribs i got that aswell, i ended up with bruising. Have u seen a doc???