I'm guessing you're not recording other people and just want to do your own thing, perhaps write some songs and record them. And you'd like to have a good idea what they sound like. Am I right? I've been doing this for a few years now. I work in a 12 x 10 room with some wall treatment that's crammed full of bookshelves (these also act as treatment) and other stuff like keyboards, guitars, computers, a rack unit, and of course monitors. Should also point out it got the Auralex treatment. The room is horrible. Welcome to the money pit.
Small rooms are a b**** to work in, and to treat. Even a treated room that size is going to have dead spots. It's the nature of
the beast. Buy a new house with a large room for mixing and get it treated. Can't afford the house payments? Okay. IK Media ARC2 system can help you out a lot. It's a lot better than the first ARC system. I'd actually go for a pair of
Yamaha HS-8s. Yamahas are more like real speakers than
reference monitors. They have good mid definition, and the thing I like about them is that the bass port is in the rear so you don't get that bass blast in your face. Pretty much if you can get a mix sounding decent on these it'll translate well elsewhere. 5" monitors will have better midrange definition, but you'll be burning a ton of CDs to take to your car etc. so you can get an idea what the bass is doing. I'd also think about investing in a subwoofer in the future. So I'd go 8" Yamahas. HS-8. Contact Sweetwater.
Keep in mind that rooms and gear take time to learn, and that you can produce a decent mix. While it might not, and probably won't compete with the commercial houses, you can do it. Don't forget to ask about the ARC2 system. The reviews are mixed, but in a small craptastic room it's a must.