How To Properly (and efficiently) Regulate Battery Inputs
If battery life is the most important factor, you should move away from LDO regulators and go switched instead; at the cost of increased noise and complexity.

By design, linear regulators waste power to drop voltage down to an intended level. This is rarely a good idea in a battery-powered environment. You can get integrated PMICs that will condition your rails from a battery source and offer other features such as protection, brown-out detection, etc. 

A quite simple solution is a pair of parallel switching regulators.

I see that you need at least 500mA maximum output and an enable line.

For down conversion, something like the 

PAM2305 series ($0.91)

And for the up conversion - 

FAN4860UC5X ($1.21)