Please recommend a non-greasy, no-wash treatment.

My hair is getting drier and thinner.

My hair, which used to be shiny even without conditioner, doesn't look good without it.

But now I feel like even the conditioner isn't enough.

I'm looking to give my hair some nourishment, and I noticed there are no-wash treatments available. It seems best to use them after washing, so could you recommend a product you use? Ideally, I'd like to try something light and non-greasy.