How can I duplicate the angle?

my daughter doesn't sleep well unless she is snuggled up in the crook of my arm or lying on a incline (she is 8 months old) how can I duplicate the angle that she likes to sleep at with out the risk that putting a pillow in her crib brings? she just seems to be more comfortable with her head and shoulders propped up. this just started to she use to sleep all night long in her crib but it seems like now when we lay her down flat in her crib she gets upset and uncomfortable. the idea I had was maybe putting a firm flat pillow under the fitted sheet in her crib?