Took me a while to figure out too! Turns out, it's easier for the smaller person to be a big spoon.
If you're larger than your partner, lay lower in the bed compared to your partner. Your face should be at their back. Pull that cushion down with you to help your neck. If they curl up a little, your arm can bend a bit forwards as it ends up at their legs, and it won't fall asleep at all.
Happy napping! ๐
That's Grant O'Brian from Dropout! Where is this from?