Breathable camera backpack

I'm looking for some input into purchasing a new camera backpack. I have a T2i, 15-85mm lens (which is usually mounted on the camera), 55-250mm lens, and I will soon have a ~30mm prime and 430EX flash (if I use hoods, they will be stored mounted backwards). I'm looking for a backpack that has the following specs in order of priority:

- Holds my camera+lenses
- Has room for non-camera stuff (i.e. extra bag space should be general purpose and not be dedicated with lens dividers, etc.)
- Is breathable on the back
- Is relatively slim (i.e. not a huge bulge on the back - I will not be using a camera with a grip)
- MAYBE has room for a 13" laptop or a pad of 8.5x11" paper - this would be nice, but is not a necessity - if the bag can fit all of my other stuff and be overall slimmer/smaller, I'd be fine with this requirement going out the window.

With all the bags out there on the market, I would have thought that there would be something that comes close to meeting these specs. Unfortunately, most of my searches have come up short. The closest thing I could find was the Kata Bumblebee UL 222 (http://www.kata-bags.com …?Version=photo&​p_Id=19780). It looks like a great bag, but it's a) a *bit* too large (but not too much - I'm nit-picking here), b) I'm not a fan of having the waist harness permanently attached, and c) is really expensive ($275, if you can find it in stock). If it were a bit cheaper and I could remove the waist harness, I would probably buy it. I really like the mesh back such that it's breathable - this makes a huge difference on hot or humid days! I also like how I can remove the camera insert to convert this into a regular backpack.

The next best bag I've found is the Tenba Messenger Photo/Laptop Daypack (http://www.bhphotovide​o.com …Photo_Laptop_Da​ypack.html). It seems pretty nice, but I'm not sure how breathable it is, and again, I'm not sure if the waist straps can be removed.

I've also looked at many other bags, notably the Kata 3N1 series, Lowepro fastpack 250, and Lowepro CompuDaypack. Sometimes, the CompuDaypack seems like the best choice, though I'm not sure how breathable it is. Note that I've tried some of these bags, but I find most camera stores in the Boston metro area don't have a large selection of bags on hand.

Does any one have any other ideas or suggestions based on your experiences?

Thanks in advance for your help!

EDIT: I would also consider a sling bag if it meets my requirements - though I'm a bit worried about the shoulder load if I'm carrying it around all day.

Mesh or no mesh, I sweat right through my shirt. Most good quality backpacks have mesh backs. Don't matter.

And if you want something good, you gotta pay.

Most bags don't have a 1 inch airgap separated by mesh like the bumblebee 222 has - check out the video review by another POTN member, it looks really nice!

https://photography-on-the.net …68987&highlight​=bumblebee

I watched the video. That is an innovative design for sure.

Not sure if I'd personally like the aluminum frame though. Probably does make it comfortable. And that's the reason it will keep it off your back. However, the mesh area is a bit small and will only keep the center of your back cool.

I also am not crazy about the bottom opening for the camera compartment. While the lenses can be held in well, that one strap across the 70-200 does not give me a sense of security.

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