[fluxon]

For eyestrain, don't forget enough sleep, hydration, breaks, maybe reading glasses, f.lux, proper low glare ambient lighting, and astigmatism (get your eyes checked at Costco - cheap & no membership required).

Craigslist is your friend for trying out monitors before you buy, then buying one, of course. So, too, is taking your laptop to the local computer store and testing (if they'll let you) several sizes and shapes. I'm comfortable (sitting) with a Dell 24" appearing above my laptop screen. Standing, I haven't made up my mind yet.

Given buying another monitor now, I'd go with IPS as others have advocated here.