13" black nylon sleeve good enough?

My toshiba would clunk around a lot in my backpack with my textbooks and i don't want my Mac to experience that.

If I get the 30$ sleeve from apple.com, and put it in my pack will i be okay? Most people use messenger bags i see but those are uncomfortable for me

You didn't say if it was a 13" Macbook Pro or 13" Macbook Air - I am going to assume the Pro

Any sleeve will help - but I'd recommend something with padding - especially in a backpack with textbooks.
Can you link to the one you are thinking about?
What is your budget?
Thule makes a good case
Thule 13" Sleeve for MacBook or MacBook Pro - Apple Store (U.S.)

I also like the hard cases - as suggested on this forum the incipio feather is quite good - has decent protection and doesn't add much heft.
MacBook Pro 13in Cases, Covers, and Sleeves by Incipio

I was looking at

Incase 13" Neoprene Pro Sleeve for MacBook Pro - Apple Store (U.S.)

But the Thule looks nice!