<p>check out the timbuk2 laptop bags for messenger style (they have options). Personally I dont think the laptop bags are as nice or as versatile as the normal messenger bags (which you can customize in every way).</p>
<p>The gap sells a small bag that meets your description but I dont know how it is on the shoulders (I dont carry mine for long when I use it). They are near end of life so they are on sale everywhere and might be gone.</p>
<p>My favorite suggestion is to use a laptop sleeve. A padded bag the size of your laptop with a handle and maybe a small pocket or two. You can stick that in ANY big you want (like say...a medium Timbuk2 bag with a center divider to meet your requirements) or just carry the sleeve when all you want is hte laptop. Timbuk2 also makes a sleeve but Booq has nicer sleeves for the same price (the vyper series).</p>