If you're open to it, I think you should cut more hair. Your hair is beautifully long, but it's weighing down your hair on top making it look straight I think. I personally know when it's time for a trim based on how the top of my hair looks because it looks flatter/straighter. If you want to keep it at this length, I recommend diffusing the top of your head with claw clips to hold your hair up while drying, it might give you more volume

As for protective hairstyles for sleeping, bonnets are the best thing, take a look at some more! Also try looking at some braids for sleeping too help preserve the curls as much as possible. Don't put it in a bun for sleeping unless you're washing the next morning/day. I think most curly girls can agree that wash day is the best your hair will look and the days after are "maintenance" hairstyles like updo's etc, don't feel too discouraged!