Prius and car seats

So, we have a 2012 Prius and having a hard time finding a convertible car seat that fits rear facing. Our 8 month old is growing out of his infant seat and we need to switch to a convertible but can't seem to find one that doesn't cause the passenger seat to be in an uncomfortable position. We just bought the Britax Boulevard but doesn't seem it will fit unless it's the passenger is almost all the way up. Has anyone found one that works in a Prius or do we have to get a new car?? Lol