another reflux question from a ftm

Hi?I'm a lurker here normally but I have a question for mamas with reflux babies. My LO was a New Years baby so she just turned 8 weeks. We have been dealing with reflux since week 3 and I still have been unable to figure out a good sleeping arrangement for night time. During the day she either naps in her swing or car seat (if we are out on errands) and that works well.

I've tried propping up her mattress in her pack n play with pillows but that doesn't work because the angle isn't right and she will wake up in pain. Or if I prop it up too much then she rolls over and is almost face down on the mattress =(. The nights she gets the most sleep is when we both fall asleep during a midnight nursing session, which means I'm on my back and she's draped over my tummy. I hate it when this happens since I'm afraid she will roll down onto my matress and into the bed covers.

 Lately I have been bed sharing with her propped up in the boppy. She gets about 3 hour stretches on the boppy with me typically waking up every 2 hours to adjust her if she falls into the hole. I don't like using the boppy for that reason but I have to sleep myself some how?.I don't like using the swing for night time since she never naps long in it anyways?,maybe 1 hour tops and then she starts squirming awake.

I know a lot of you use the rock n play but I'm too afraid of the flat head issues I have read about to purchase one. Also we are kind short on cash with me being on leave so that rules out that option. 

We just started zantac and I haven't seen a difference yet in her being able to sleep on her back in a flat mattress. My question is this: how long did it take for you to see a difference once your baby was on zantac? Were they ever able to sleep flat on their back or did you just have to wait for LO to grow out of it?

tia!

(ps: I apologize for spelling mistakes, I'm typing one handed and my contacts are off lol)