Second/Dual Monitor for my iMac (late 2013)

Hi everyone. I am researching for a second monitor to compliment my iMac and hoping for some advice or if you have a second monitor, what do you use? I need it for my work as I am constantly going back and forth from spreadsheets, documents, the internet and to my email. So this monitor won't be used for photo editing or anything high end like that. However, I don't want something where I see a huge difference in quality/clarity. I am looking at the Dell U2312HM which I can still find online but not sure if that is overkill. I am also looking for a monitor that has a DisplayPort for simple hook up to the iMac (knowing I will have to get an adapter). I work from home so this extra monitor needs to last as I think I live at my desk (ha ha). So thank you in advance for all responses. Cheers!