MacBook Air 2015 Model - Energy Saving woes

I seem to have a frustrating issue with my new macbook air (13") running Yosemite 10.10.3 with the sleep display option.

I have only one scale - sleep display and do not have a computer display scale.

My issue is - If I set the sleep display to 1min or if I close the lid, the system disconnects me from wifi and all other work apps and goes to sleep. (setting the screen sleep to never is not an option as that drains my battery and lasts about 4hrs). I do need the screen to sleep but not the computer.

Is there anyway to set screen to sleep but not computer to sleep? ( I dont have the put computer to sleep scale in energy saver settings)?

Are there any 3rd party tools available to over-ride this and manage the settings?