Here's a simple way to make your voice-over reads more natural sounding; take your headphones off when you record. The problem with wearing them in your home studio booth is, too often, voice talents get use to listening to their own voice in the headphones as they record. I've been taking my headphones off for years and have never regretted it. Especially for those jobs where they want a conversational tone, like e Learning. Overloading your ears with sound is not going to be beneficial.
Now, that said, sometimes you must wear them. If you're at a recording session, you'll need to have them on so as to be able to hear input from the director who is outside your booth; usually looking at you through glass. You can turn the volume of the headphones down a bit as you read script.
I know. I know! You like the sound of your own voice flooding through your headphones and into your ears when you record. You're comfortable that way. Let me ask you something. What exactly are you listening for when you put on headphones inside your home studio booth? While you stumble and bumble to come up with a legitimate answer, I would suggest you try an experiment; take your headphones off in your recording booth. If you're in love with the sound of your own voice with your headphones on, you'll probably be uncomfortable for a while. Stay with it! Your reads will benefit.
If you're editing audio, of course, you'll want to have your headphones on to check for unwanted mouth clicks and any other undesirable sounds you can edit out. Sometimes studio monitors will not give you super accurate feedback. With your headphones on while editing, you'll hear things you won't hear on your monitors.
A good set of headphones is a must for any studio. I use Audio-Technica. But there are a ton of different, quality brands out there. Sony, Beyerdynamic and Sennheiser come to mind. Do some research online before buying. Stay away from "cheap" headphones. Not all are created equal. Over the years, I've used Broadcast Supply Worldwide to buy my studio equipment and have been pleased with the price, quality, and on-time delivery. Here's a link to their headphone offerings.