Going from Stereo to...4.0?

Hi guys! So for quite a bunch of years, my main home cinema setup has been a Pioneer amp VSX-823K, paired with a couple of Mission MX2 speakers...and a 55inch Sony TV. No subwoofer, no central channel either. Nothing too special, but since the room I watch from is rather small, it does the job pretty well. This is my home cinema/gaming station, and it's all hooked to a gaming PC.

So, I'm considering to add maybe a couple of tiny rear speakers to provide surround sound (ish? 4.0, I guess). Now the problem is, I literally have no space. I have an L-shaped Ikea sofa that takes one corner completely, and leaves not much space at all on the other. I was thinking maybe tiny satellites hanging from a pole that goes straight into the edge of the corner, behind the sofa's corner...So something small anyway, as they'd be rather close to the head/ears of the viewers (me/parner's/friends). I'm not sure what to look for...I'm looking for something small that can deliver decent sound quality without having to be too loud. What would be your advice?

Thanks!