Can't give any advice on monitors because I've only ever tried a few different ones.
But just about anything will be a major step up from (normal) desktop speakers.
One reason I haven't upgraded to monitors is because I've gotten to know these speakers so well, I have little to no trouble getting my mixes to translate well.
So that is the most important thing I would say when getting monitors.
While Behringger isn't exactly a reputable brand for most of their products, their Truth monitors actually get good responses from online reviews and others in this forum.
You may want to consider those, and search this forum for threads about them.
I would go with something that's comfortable to listen to, and not worry TOO much about a perfectly flat response, as long as you can get used to them and learn how they sound on different songs, so you can make your mixes translate.
And of course treat your room if you haven't already.