Originally posted by FantasticMrFox Have a look at f-stop's Mountain range of backpacks. Targeted at photographers, you choose your backpack and a camera insert (called ICU) the right size for your gear. The ICU can be secured within the backpack and access is through the back panel. You can use the backpack with a range of different sized ICUs, or without any just as a normal backpack.
I have the Loka (predecessor of the current Ajna model) and it's amazing. Comfortable to wear, loads of smart features and an extremely high material and manufacturing quality. I wrote a review for my website which you can check out. But for your needs the Lotus might be a better size.
I have this same model and I support everything Mr Fox said here. I also find it more comfortable than Lowepro bags even when completely stuffed with camera gear.