If you're only recording voice-overs, and not making mixing decisions that affect how much bass is in a song mix, you don't need a lot of treatment. Simply enclose / surround the smaller area you record and listen in with absorption.
I do see one problem with your setup though - you have a reflecting wall right behind you. You'll do better to flip your speakers 180 degrees, so they're near the wall pointing out into the room. More here:
How to set up a room
--Ethan