How do you get hair that is sleek but wavy?

[TheYamiOfYawn]

My hair is naturally messy - very thick, wavy in places but flat in others, a bit like a lion's mane. If I straighten it and use oil or serum it looks pretty good, and it has enough natural wave and volume that even straightened it doesn't look flat, just neat. If this is what my hair does best, I'll stick with it, but I do like that sleek but wavy, more relaxed look. How can I achieve it without a gazillion prodicts?

[AliceinSlumberland]

You could try washing your hair at night and sleep with it in two French plaits. You look ridiculous but as long as you don't brush it when you get up (just run your fingers through) then it stays quite sleek.

[ClaraDeLaNoche]

I think you have hair like me! I straighten then wave. Need to let the curls drop which they should do because of the straighteners. I like heated rollers or BByliss Pro Perfect curl on the lowest heat.