No insert needed, just keep it fluid
The four compartment insert is not a stationary thing, it needs to float inside the bag so you can adapt different needs on different days. So we don't want or need a one compartment insert.
In my bag I take the foam out from one side (front side) of the insert so I can bend/fold the insert into a V or L shape when I want to put the camera with a longer lens on the body. Gives me some added flexibility when I'm in a hurry to hide the camera, or simply when I come back from a long day shooting and want to store everything quickly inside the bag.
It you're worried about protection, the canvas is better protected, because it non abrasive and pulls everything tightly together. This eliminates lens shades falling off or damage when a stiff bag lets equipment bounce around inside.
It's good just the way it is.
As far as attaching a tripod, most find it makes the bag too heavy and it's easier to carry it in a separate bag. Strapping a tripod to the bottom also makes it hard to set down and you are always poking into someone.
Once upon a time we had Velcro loops sewn onto the shoulder strap to fasten a monopod, so it hung down from the shoulder and wouldn't poke anyone. It you like this idea, you can get some Velcro ties at a boat supply store and lash the monopod to the shoulder strap. Tripod is too heavy.